Electrode body and secondary battery

Abstract

To secure high peel strength.SOLUTION: An electrode sheet 35 in an electrode body 10 of a secondary battery 1 includes a base material 36 to serve as a current collector 31, a mixture layer 50 including an electrode active material 72 formed on this base material 36, and an insulating layer 60 containing an insulating material formed on the base material 36 adjacent to this mixture layer 50. At a border region α between the mixture layer 50 and the insulating layer 60, a mixture layer 50x extends in an overlapping manner over an insulating layer 60x that covers a surface 36s of the base material 36. On a border surface S of the insulating layer 60 for the mixture layer 50x, a plurality of uneven parts 70 with a larger uneven width W than a particle diameter R of the electrode active material 72 are arranged side by side.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an electrode assembly and a secondary battery. [Background technology]

[0002] Conventionally, some electrode bodies for secondary batteries include a substrate serving as a current collector and a composite layer containing an electrode active material formed on the substrate. Furthermore, in such electrode bodies, an uncoated portion set at an end of the substrate serves as a connection portion with an electrode terminal. For example, as shown in Patent Document 1, some electrode bodies include an insulating layer containing an insulating material formed on the substrate adjacent to the composite layer at the position that will become the uncoated portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-76196 Summary of the Invention [Problem to be solved by the invention]

[0004] In an electrode assembly having the above-described configuration, peeling tends to occur at the edge of the composite layer formed on the substrate, and therefore it is important to ensure high peel strength at the edge of the composite layer, i.e., the boundary region with the insulating layer. [Means for solving the problem]

[0005] Various aspects of the electrode assembly and secondary battery that solve the above problems will be described. Aspect 1 is an electrode body comprising a substrate serving as a current collector, a composite layer containing an electrode active material formed on the substrate, and an insulating layer containing an insulating material formed on the substrate adjacent to the composite layer, wherein in the boundary region between the composite layer and the insulating layer, the composite layer extends above the insulating layer covering the surface of the substrate, and a plurality of irregularities are arranged side by side on the boundary surface of the insulating layer relative to the composite layer, the irregularities having an irregularity width greater than the particle diameter of the electrode active material.

[0006] That is, by covering the surface of the substrate with an insulating layer in which the binder content can be easily increased, the insulating layer can be strongly bonded to the substrate at the boundary region between the composite layer and the insulating layer. Furthermore, by providing fine irregularities on the boundary surface of the insulating layer with respect to the composite layer, the contact area between them can be enlarged. This increases the bonding strength of the composite layer to the insulating layer, thereby ensuring high peel strength at the boundary region.

[0007] In particular, by setting the unevenness width at the boundary surface to a value larger than the particle diameter of the electrode active material, the electrode active material in the composite layer can easily enter the recessed shape. That is, the binder in the composite layer exists in a state of adhering to the electrode active material. Therefore, with the above configuration, the substantial contact area between the insulating layer and the composite layer can be effectively expanded. This further strengthens the bonding of the composite layer to the insulating layer, thereby ensuring even higher peel strength.

[0008] A second aspect is the electrode assembly according to the first aspect, wherein the width of the irregularities is 5 to 30 times the particle diameter. A third aspect is the electrode assembly according to the first or second aspect, wherein the unevenness width is 20 μm or more and 120 μm or less.

[0009] A fourth aspect of the present invention is the electrode assembly according to any one of the first to third aspects, in which the unevenness accounts for 20% or more of the boundary surface. According to the above-mentioned configurations, high peel strength can be ensured in the boundary region.

[0010] A fifth aspect is the electrode assembly according to any one of the first to fourth aspects, wherein the thickness of the insulating layer at the bottom of the irregularities is greater than the particle diameter of the insulating material. According to the above-mentioned configuration, the insulating material can be present even at the bottom of the irregularities where the thickness of the insulating layer is thin, and this allows the insulating layer having irregularities at the boundary surface with the composite layer to function properly as an insulating layer.

[0011] A sixth aspect is the electrode assembly according to any one of the first to fifth aspects, wherein the irregularities are present within 200 μm of the tip of the composite layer overlapping the insulating layer. That is, in the boundary region, the applied composite paste flows, which tends to thin the composite layer. This results in uneven distribution of the binder, which makes the composite layer more likely to peel off. However, with the above configuration, unevenness is formed on the boundary surface of the insulating layer relative to the composite layer in the area where such thinning is likely to occur. This effectively increases the peel strength of the composite layer in the boundary region.

[0012] A seventh aspect is the electrode assembly according to any one of the first to sixth aspects, in which the composite layer is a positive electrode active material layer. According to the above configuration, a high-quality electrode body for a positive electrode can be formed.

[0013] An eighth aspect is a secondary battery including the electrode assembly according to any one of the first to seventh aspects. According to the above configuration, a high-quality secondary battery can be formed. [Effects of the Invention]

[0014] According to the present invention, high peel strength can be ensured. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view of a secondary battery. [Figure 2] FIG. [Figure 3] FIG. 2 is a side view of the secondary battery. [Figure 4] FIG. 2 is a cross-sectional view of a composite layer and an insulating layer formed on a substrate. [Figure 5] FIG. 2 is an enlarged cross-sectional view showing the laminated structure of the composite layer and the insulating layer in the boundary region. [Figure 6] FIG. 10 is a schematic diagram of a comparative example showing a boundary surface when the unevenness width is narrow. [Figure 7] 1 is a graph showing the relationship between unevenness width and peel strength. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of a secondary battery and an electrode assembly thereof will be described with reference to the drawings. (Secondary battery) 1, the secondary battery 1 includes an electrode assembly 10 in which a positive electrode 3, a negative electrode 4, and a separator 5 are integrated, and a case 20 that houses the electrode assembly 10. The secondary battery 1 of this embodiment has a configuration as a lithium ion secondary battery in which the electrode assembly 10 inside the case 20 is impregnated with a non-aqueous electrolyte solution (not shown).

[0017] More specifically, in the secondary battery 1 of this embodiment, the positive electrode 3, the negative electrode 4, and the separator 5 are stacked in a sheet-like outer shape. Then, by winding up the stack of the positive electrode 3, the negative electrode 4, and the separator 5, an electrode assembly 10 is formed in which the positive and negative electrodes and the separators 5 are alternately arranged in the radial direction with the separator 5 sandwiched between the positive electrode 3 and the negative electrode 4.

[0018] The case 20 of this embodiment includes a case body 21 in the shape of a flat, generally rectangular box, and a lid member 22 that closes an open end 21x of the case body 21. The electrode body 10 of this embodiment has a flat outer shape that corresponds to the box shape of the case 20.

[0019] (Electrode sheet and electrode body) More specifically, as shown in FIG. 2, in the secondary battery 1 of this embodiment, the positive electrode 3 and the negative electrode 4 each have a configuration as an electrode sheet 35 including a current collector 31 having a sheet-like outer shape and an electrode active material layer 32 laminated on this current collector 31.

[0020] Specifically, for the electrode sheet 35P for the positive electrode 3, a composite paste 37P containing a lithium transition metal oxide as the positive electrode active material is applied to a substrate 36P made of aluminum or the like that constitutes the positive electrode current collector 31P. For the electrode sheet 35N for the negative electrode 4, a composite paste 37N containing a carbon-based material that serves as the negative electrode active material is applied to a substrate 36N made of copper or the like that constitutes the negative electrode current collector 31N. Each of the composite pastes 37P and 37N further contains a binder. In the secondary battery 1 of this embodiment, the composite pastes 37P and 37N are dried to form corresponding positive electrode active material layers 32P and negative electrode active material layers 32N on the positive and negative electrode sheets 35P and 35N, respectively.

[0021] Furthermore, in the secondary battery 1 of this embodiment, the positive and negative electrode sheets 35P, 35N are each shaped like a strip. The electrode body 10 of this embodiment is configured such that the positive and negative electrode sheets 35P, 35N are stacked with the separator 5 sandwiched between them and wound around a winding axis L that extends in the width direction of the strip (the left-right direction in FIG. 2).

[0022] 2, the separator 5 and each electrode sheet 35 are wound in such a way that the electrode sheet 35P constituting the positive electrode 3 is wound on the inside. However, this figure is one example showing the structure of the electrode assembly 10, and the separator 5 and each electrode sheet 35 may also be wound in such a way that the electrode sheet 35N constituting the negative electrode 4 is wound on the inside. This determines whether the electrode sheet 35 arranged on the outermost shell of the electrode assembly 10 is the electrode sheet 35P constituting the positive electrode 3 or the electrode sheet 35N constituting the negative electrode 4.

[0023] 1 to 3, the lid member 22 of the case 20 is provided with a positive electrode terminal 38P and a negative electrode terminal 38N that protrude outside the case 20. Furthermore, each electrode sheet 35 has an uncoated portion 39 where the electrode active material layer 32 is not formed on the current collector 31. The secondary battery 1 of this embodiment is configured such that, by utilizing these uncoated portions 39, the electrode sheet 35P constituting the positive electrode 3 and the positive electrode terminal 38P are electrically connected, and the electrode sheet 35N constituting the negative electrode 4 and the negative electrode terminal 38N are electrically connected.

[0024] Specifically, the electrode body 10 of this embodiment is housed in the case 20 with its winding axis L aligned along the longitudinal direction (left-right direction in FIG. 1 ) of the lid member 22, which is an elongated, generally rectangular plate. Furthermore, in this state, an uncoated portion 39P of an electrode sheet 35P constituting the positive electrode 3 is connected to a positive electrode terminal 38P via a connecting member 40P. Similarly, an uncoated portion 39N of an electrode sheet 35N constituting the negative electrode 4 is connected to a negative electrode terminal 38N via a connecting member 40N.

[0025] Furthermore, an electrolyte solution 41 is poured into the case 20. That is, the electrolyte solution 41 of the secondary battery 1 configured as a lithium ion secondary battery is one in which a lithium salt serving as a supporting salt is dissolved in an organic solvent. Thus, the secondary battery 1 of this embodiment is configured such that the electrode assembly 10 sealed in the case 20 is impregnated with the electrolyte solution 41.

[0026] (composite layer and insulating layer) As shown in FIG. 4, in the secondary battery 1 of this embodiment, the electrode active material layer 32 of the electrode sheet 35 constituting the electrode body 10 has a configuration as a composite layer 50 obtained by applying a composite paste 37 containing an electrode active material onto a substrate 36 that serves as the current collector 31, as described above.

[0027] More specifically, the electrode sheet 35 shown in Fig. 4 is an electrode sheet 35P for a positive electrode 3, which has a positive electrode active material layer 32P formed on a substrate 36P that serves as a positive electrode current collector 31P. The electrode sheet 35 also has an insulating layer 60 provided on the substrate 36 adjacent to the composite layer 50. That is, the insulating layer 60 is formed in a position that partially covers an uncoated portion 39 set at a widthwise end of the strip-like foil electrode sheet 35. In the secondary battery 1 of this embodiment, the insulating layer 60 is also formed by applying an insulating paste 61 containing an insulating material onto the substrate 36.

[0028] In the secondary battery 1 of the present embodiment, the composite paste 37 and the insulating paste 61 are simultaneously applied to the base material 36. When the composite paste 37 and the insulating paste 61 are dried, the composite layer 50 and the insulating layer 60 are formed adjacent to each other on the base material 36.

[0029] (Roughness of boundary area and boundary surface) 4 and 5, the electrode sheet 35 of this embodiment is configured such that, in a boundary region α where the composite layer 50 and the insulating layer 60 are adjacent to each other, the insulating layer 60x covers the surface 36s of the base material 36. Furthermore, in this boundary region α, the composite layer 50x extends above the insulating layer 60x to overlap it. As a result, the electrode sheet 35 of this embodiment is configured such that the upper surface 60xs of the insulating layer 60x forms a boundary surface S with the composite layer 50x stacked above the insulating layer 60x.

[0030] Furthermore, in the electrode sheet 35 of this embodiment, the upper surface 60xs of the insulating layer 60x, which forms the boundary surface S with respect to the composite layer 50x, is provided with a plurality of asperities 70 arranged side by side, each having an asperity width W greater than the particle diameter R of the electrode active material 72 contained in the composite layer 50x (W>R). The electrode sheet 35 of this embodiment thereby increases the surface area of ​​the insulating layer 60x in contact with the composite layer 50x, i.e., the contact area, thereby increasing the peel strength of the composite layer 50x laminated on the insulating layer 60x. In other words, the insulating layer 60x arranged in the boundary region α has a structure that makes it difficult to peel off.

[0031] The term "peel strength" can also be rephrased as "peel resistance strength" or "bonding strength." The unevenness width W at the boundary surface S of the insulating layer 60x relative to the composite layer 50x can be measured, for example, using a scanning electron microscope (SEM). Specifically, a cross-sectional image of the boundary region α between the composite layer 50 and the insulating layer 60 is captured. The compositions of FIGS. 4 and 5 are based on the cross-sectional image of the boundary region α captured at this time. Then, by analyzing this cross-sectional image, the distance between two adjacent recessed shapes 73, 73, specifically the distance between the bottoms 73b, 73b of each recessed shape 73, 73, can be measured as the unevenness width W.

[0032] That is, the "arrangement" of the irregularities 70 on the boundary surface S of the insulating layer 60x with respect to the composite layer 50x is basically random. For this reason, in the electrode sheet 35 of this embodiment, the "irregularity width W" measured as described above is used as an index representing the size of the irregularities 70.

[0033] More specifically, in the electrode sheet 35 of this embodiment, the particle diameter R of the electrode active material 72 contained in the composite layer 50 is set to, for example, a range of 3 μm or more and 5 μm or less. Note that this value applies when the electrode sheet 35 is the electrode sheet 35P on the positive electrode 3 side, that is, when the composite layer 50 contains the positive electrode active material 72P. Furthermore, the irregularity width W at the boundary surface S is set to, for example, a range of 40 μm or more and 80 μm or less. When expressed in comparison with the particle diameter R of the electrode active material 72, the set range of this irregularity width W corresponds to a range of 10 to 20 times the particle diameter R.

[0034] That is, the peel strength of the composite layer 50x laminated on the insulating layer 60x increases as the contact area between the composite layer 50x and the insulating layer 60x increases. This contact area can be expanded by forming minute irregularities 70 on the boundary surface S.

[0035] However, as shown in FIG. 6 , if the unevenness width W at the boundary surface S is too narrow, the electrode active material 72 will have difficulty penetrating into the recessed shapes 73. That is, the binding strength of the composite layer 50x to the insulating layer 60x is due to a binder (not shown) contained in the composite layer 50x. Furthermore, in the composite layer 50x, the binder exists in a state of adhering to the electrode active material 72 (not shown). Therefore, if the electrode active material 72 in the composite layer 50x cannot enter the recessed shapes 73 of the unevenness 70 as described above, the effective contact area between the insulating layer 60x and the composite layer 50x will be smaller than the contact area when the boundary surface S is flat. This reduces the binding strength of the composite layer 50x to the insulating layer 60x. As a result, there is a possibility that the effect of improving the peel strength will not be obtained.

[0036] Specifically, as shown in Fig. 7, when the particle diameter R of the electrode active material 72 contained in the composite layer 50 is equivalent to that of the electrode sheet 35 of this embodiment, the peel strength is improved when the irregularity width W at the boundary surface S is generally in the range of 10 µm or more and 150 µm or less. Furthermore, the lower limit of the irregularity width W is preferably 20 µm or more, and more preferably 40 µm or more. The upper limit of the irregularity width W is preferably 120 µm or less, and more preferably 80 µm or less.

[0037] 7 shows the peel strength values ​​corresponding to the irregularity width W at the boundary surface S, where the boundary surface S of the insulating layer 60x relative to the composite layer 50x is set to "100" when the boundary surface S is a "flat surface." Furthermore, when expressed relative to the particle diameter R of the electrode active material 72, the irregularity width W ranges of "10 μm or more," "20 μm or more," and "40 μm or more" correspond to approximately "2.5 times or more," "5 times or more," and "10 times or more," respectively. Furthermore, the irregularity width W ranges of "150 μm or less," "120 μm or less," and "80 μm or less" correspond to approximately "37.5 times or less," "30 times or less," and "20 times or less," respectively. In the electrode sheet 35 of this embodiment, the set range of the irregularity width W is specified as described above based on the test results shown in FIG. 7.

[0038] More specifically, the effect of improving the peel strength is obtained when the proportion of the asperities 70 in the boundary surface S of the insulating layer 60x relative to the composite layer 50x is approximately 20% or more. Furthermore, it is estimated that the greater the proportion of the asperities 70, the more significant the effect of improving the peel strength. However, if the proportion of the asperities 70 is, for example, 70% or more, it becomes difficult to ensure stable quality. For this reason, the proportion of the asperities 70 in the boundary surface S is preferably 30% or more, and more preferably 50% or more. The electrode sheet 35 of this embodiment is configured so that the boundary surface S of the insulating layer 60x relative to the composite layer 50x has asperities 70 with such a preferable proportion.

[0039] Furthermore, the thickness D of the insulating layer 60x at the bottoms of the asperities 70, i.e., the bottoms 73b of the recessed shapes 73, is set to a value larger than the particle diameter r of the insulating material (not shown) contained in the insulating layer 60x (see FIG. 5 , D>r). That is, the formation of areas where the insulating material is absent results in a decrease in the insulating performance. In light of this, in the electrode sheet 35 of this embodiment, the thickness D of the insulating layer 60x at the bottoms 73b of the recessed shapes 73 is set to, for example, 2 μm or more. The particle diameter of the insulating material, boehmite, is generally 1 μm or more and 3 μm or less, and the thickness D of the insulating layer 60x at the bottoms of the asperities 70 is set to a value taking into account this particle diameter r. As a result, in the electrode sheet 35 of this embodiment, the insulating layer 60x having the asperities 70 at the boundary surface S with respect to the composite layer 50x properly functions as the insulating layer 60.

[0040] Furthermore, the difference between the bottom 73b of the recessed shape 73 and the top 74a of the protruding shape 74 in the thickness direction of the insulating layer 60x is defined as the height H of the irregularities 70. In the electrode sheet 35 of this embodiment, the height H of the irregularities 70 is approximately three times or more the particle diameter R of the electrode active material 72.

[0041] In addition, in the electrode sheet 35 of this embodiment, the insulating layer 60x in the boundary region α has an irregularity 70 formed on its boundary surface S within approximately 200 μm of the tip portion 50xa of the composite layer 50x formed above and overlapping this insulating layer 60x.

[0042] That is, in the boundary region α, the thickness of the composite layer 50x formed therein is likely to be thinned due to the flow of the composite paste 37. Furthermore, in such a thinned portion, the composite paste 37 dries quickly, which tends to cause uneven distribution of the binder contained in the formed composite layer 50x. This may result in a decrease in the peel strength of the composite layer 50x.

[0043] In the electrode sheet 35 of this embodiment, the thinned region β, where the peel strength is likely to decrease, is likely to be formed within 200 μm from the tip end 50xa of the composite layer 50x. That is, the electrode sheet 35 of this embodiment has irregularities 70 formed on the boundary surface S of the insulating layer 60x relative to the composite layer 50x in the thinned region β. This effectively increases the peel strength of the composite layer 50.

[0044] (manufacturing process) In the secondary battery 1 of this embodiment, when manufacturing the electrode sheet 35P for the positive electrode 3 as the electrode sheet 35 constituting the electrode body 10, the viscosity of the insulating paste 61 is set to, for example, 1000 mPa·s or more and 5000 mPa·s or less. The reference temperature for viscosity measurement is 25°C. At this time, the solid content of the insulating paste 61 is set to, for example, 10% or more and 40% or less. Furthermore, the viscosity of the composite paste 37P for the positive electrode 3 is set to, for example, 100 mPa·s or more and 20000 mPa·s or less. At this time, the solid content of the composite paste 37P is set to, for example, 60% or more and 70% or less.

[0045] As described above, the composite layer 50 and the insulating layer 60 are formed by simultaneously applying the composite paste 37P and the insulating paste 61 to the substrate 36. The discharge rate of the composite paste 37P is set to, for example, 500 g / min or more and 2000 g / min or less. The discharge rate of the insulating paste 61 is set to, for example, 10 g / min or more and 100 g / min or less.

[0046] Furthermore, when the composite paste 37 and the insulating paste 61 are applied, the viscosity of the insulating paste 61 is set to be lower than the viscosity of the composite paste 37. That is, by setting the fluidity of the insulating paste 61 to be high, the insulating paste 61 applied to the base material 36 is more likely to flow and spread over the base material 36. In the electrode sheet 35 of this embodiment, this allows the composite layer 50x to overlap and extend above the insulating layer 60x covering the surface 36s of the base material 36, forming a boundary region α between the composite layer 50 and the insulating layer 60.

[0047] Furthermore, in the electrode sheet 35 of this embodiment, the irregularities 70 are formed on the boundary surface S of the insulating layer 60x relative to the composite layer 50x in accordance with the specifications of each material listed above, including the particle diameter R of the electrode active material 72 and the particle diameter r of the insulating material, and manufacturing conditions such as temperature. The electrode sheet 35 of this embodiment is configured to optimize the irregularities 70 formed on the boundary surface S of the insulating layer 60x by appropriately adjusting each of these parameters.

[0048] (action) By providing a plurality of asperities 70 arranged side by side on the boundary surface S of the insulating layer 60x relative to the composite layer 50x, the contact area between the composite layer 50x and the insulating layer 60x is increased. Furthermore, this increased contact area increases the adhesive strength of the composite layer 50x to the insulating layer 60x. As a result, the composite layer 50x that overlaps and extends above the insulating layer 60x in the boundary region α between the composite layer 50x and the insulating layer 60x is less likely to peel off.

[0049] Next, the effects of this embodiment will be described. (1) The electrode sheet 35 constituting the electrode body 10 of the secondary battery 1 includes a substrate 36 that serves as the current collector 31, a composite layer 50 containing an electrode active material 72 formed on the substrate 36, and an insulating layer 60 containing an insulating material formed on the substrate 36 adjacent to the composite layer 50. In a boundary region α between the composite layer 50 and the insulating layer 60, the composite layer 50x extends above and overlaps the insulating layer 60x that covers the surface 36s of the substrate 36. A plurality of asperities 70, each having an asperity width W greater than the particle diameter R of the electrode active material 72, are arranged side by side on the boundary surface S of the insulating layer 60 relative to the composite layer 50x.

[0050] That is, by covering the surface 36s of the base material 36 with the insulating layer 60x, which has an easily increased binder content, the insulating layer 60x can be strongly bonded to the base material 36 in the boundary region α between the composite layer 50 and the insulating layer 60. Furthermore, by providing minute irregularities 70 on the boundary surface S of the insulating layer 60x with the composite layer 50x, the contact area therebetween can be increased. This increases the adhesive strength of the composite layer 50x with the insulating layer 60x, thereby ensuring high peel strength in the boundary region α.

[0051] In particular, by setting the unevenness width W at the boundary surface S to a value larger than the particle diameter R of the electrode active material 72, the electrode active material 72 in the composite layer 50x can easily enter the recessed shapes 73. That is, the binder in the composite layer 50x exists in a state of adhering to the electrode active material 72. Therefore, the above configuration can effectively increase the substantial contact area between the insulating layer 60x and the composite layer 50x. This can then strongly bond the composite layer 50x to the insulating layer 60x, thereby ensuring even higher peel strength.

[0052] (2) Specifically, for example, the unevenness width W on the boundary surface S is preferably set in the range of 10 μm to 150 μm, more preferably 20 μm to 120 μm. By setting the unevenness width W in the range of 40 μm to 80 μm, a more significant improvement in peel strength can be achieved.

[0053] (3) Furthermore, when expressed in comparison with the particle diameter R of the electrode active material 72, the setting range of the irregularity width W is preferably set to a range equivalent to, for example, 2.5 to 40 times the particle diameter R, and more preferably set to a range equivalent to 5 to 40 times the particle diameter R. Furthermore, by setting the irregularity width W to a range equivalent to 10 to 20 times the particle diameter R, a more significant improvement in peel strength can be achieved.

[0054] (4) The proportion of the irregularities 70 in the boundary surface S is preferably 20% or more, and more preferably 30% or more. Furthermore, the proportion of the irregularities 70 in the boundary surface S is even more preferably 50% or more. This increases the contact area between the composite layer 50x and the insulating layer 60x, thereby ensuring high peel strength.

[0055] (5) The thickness D of the insulating layer 60x at the bottom 73b of the recessed shape 73, which is the bottom of the irregularity 70, is larger than the particle diameter r of the insulating material contained in the insulating layer 60x (D>r). According to the above configuration, the insulating material can be present also at the bottom of the irregularities 70 where the thickness D of the insulating layer 60x is thinner. This allows the insulating layer 60x having the irregularities 70 on the boundary surface S with the composite layer 50x to function properly as the insulating layer 60.

[0056] (6) The electrode sheet 35 has irregularities 70 formed on the boundary surface S of the insulating layer 60x relative to the composite layer 50x within 200 μm from the tip 50xa of the composite layer 50x overlapping the insulating layer 60x.

[0057] That is, in the boundary region α, the applied composite paste 37 flows, which tends to thin the composite layer 50x. This results in uneven distribution of the binder, which tends to make the composite layer 50x more likely to peel off. However, with the above configuration, in the thinning range β, irregularities 70 are formed on the boundary surface S of the insulating layer 60x relative to the composite layer 50x. This effectively increases the peel strength of the composite layer 50 in the boundary region α.

[0058] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0059] The setting range of the unevenness width W may be changed as desired. The upper limit may be changed. The lower limit may be changed. Furthermore, the upper and lower limits may be changed. Furthermore, the thickness D of the insulating layer 60x at the bottom of the unevenness 70 and the height H of the unevenness 70 may also be changed as desired.

[0060] Furthermore, the boundary surface S of the insulating layer 60x with respect to the composite layer 50x may include a flat portion. That is, the entire boundary surface S does not necessarily have to have the irregularities 70. The proportion of the irregularities 70 in the boundary surface S may also be changed as desired.

[0061] In the above embodiment, the composite paste 37 and the insulating paste 61 are simultaneously applied to the substrate 36, but the application timings may be staggered. Furthermore, various settings related to the formation of the composite layer 50 and the insulating layer 60 may also be adjusted as desired.

[0062] That is, a boundary region α between the composite layer 50 and the insulating layer 60 is formed in such a manner that the composite layer 50x extends above the insulating layer 60x that covers the surface 36s of the base material 36. Then, it is only necessary to create a state in which a plurality of asperities 70 having an asperity width W larger than the particle diameter R of the electrode active material 72 are arranged side by side on the boundary surface S of the insulating layer 60 relative to the composite layer 50x. In other words, the details of the process of forming the composite layer 50 and the insulating layer 60 may be changed as desired, as long as reproducibility under the same control conditions can be ensured.

[0063] In the above embodiment, a preferred laminate structure was described for the boundary region α between the composite layer 50 and the insulating layer 60 formed on the substrate 36, using the electrode sheet 35P for the positive electrode 3 as an example, which has the positive electrode active material layer 32P formed on the substrate 36P that becomes the positive electrode current collector 31P. However, the present invention is not limited to this, and may also be applied to an electrode sheet 35N for the negative electrode 4, which has the negative electrode active material layer 32N formed on the substrate 36N that becomes the negative electrode current collector 31N.

[0064] The compositions of the composite paste 37 and the insulating paste 61, including the electrode active material, insulating material, and binder, may be changed as appropriate. Furthermore, in the above embodiment, the electrode assembly 10 is formed by winding up the positive and negative electrode sheets 35P, 35N stacked with the separator 5 sandwiched therebetween. However, this is not limiting, and the electrode assembly 10 may be applied to a stacked electrode assembly 10 having a plurality of electrode plate groups. Furthermore, the secondary battery 1 to which the electrode assembly 10 is applied does not necessarily have to be a lithium ion secondary battery, and may be applied to other non-aqueous electrolyte secondary batteries. Furthermore, the electrode assembly 10 may be applied to secondary batteries other than non-aqueous electrolyte secondary batteries.

[0065] The shape of the external terminals is not limited to the shape shown in Fig. 1 and may be changed as desired. The shape of the case 20 that forms the outer shape of the secondary battery 1 is also not necessarily limited to a flat rectangular box shape and may be changed as desired, for example, to a cylindrical shape.

[0066] Next, the technical ideas that can be understood from the above-described embodiment and modified examples will be described. (i) The unevenness width is 10 μm or more. (b) The unevenness width is 40 μm or more.

[0067] (C) The unevenness width is 150 μm or less. (iv) The unevenness width is 80 μm or less. According to the above-mentioned configurations, high peel strength can be ensured in the boundary region. [Explanation of symbols]

[0068] 1…Secondary battery 10...Electrode body 31...Current collector 35...Electrode sheet 36...Base material 36s…Surface 50,50x…Mixture layer 60,60x...insulating layer 70…Unevenness 72...electrode active material R: particle size α…boundary area S…Boundary surface W…Irregularity width

Claims

1. a substrate serving as a current collector; a composite layer containing an electrode active material formed on the substrate; an insulating layer including an insulating material formed on the substrate adjacent to the composite layer, In the boundary region between the composite layer and the insulating layer, the composite layer extends above the insulating layer covering the surface of the base material, overlapping the insulating layer; a plurality of irregularities having an irregularity width larger than a particle diameter of the electrode active material are arranged side by side on a boundary surface of the insulating layer relative to the composite layer, the thickness of the insulating layer at the bottom of the irregularities is greater than the particle diameter of the insulating material; The electrode body has a width of the unevenness of 20 μm or more and 120 μm or less.

2. 2. The electrode assembly according to claim 1, wherein the width of the irregularities is 5 to 30 times the particle diameter.

3. The ratio of the irregularities to the boundary surface is 20% or more. The electrode assembly according to claim 1 .

4. The electrode body according to claim 1 , wherein the irregularities are present within 200 μm from the tip of the composite layer overlapping the insulating layer.

5. The electrode assembly according to claim 1 , wherein the composite layer is a positive electrode active material layer.

6. A secondary battery comprising the electrode assembly according to any one of claims 1 to 5.

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