Battery cell assembly and battery comprising the same

Abstract

The application relates to the technical field of batteries, and particularly discloses a battery cell assembly and a battery comprising the same. The battery cell assembly comprises a first diaphragm, a negative electrode sheet, a second diaphragm and a positive electrode sheet which are sequentially stacked and wound; the first diaphragm and the second diaphragm are mutually bonded with the negative electrode sheet to form a first composite area; the positive electrode sheet is mutually bonded with the second diaphragm in at least a partial area to form at least one second composite area; and the length of the second composite area is smaller than that of the first composite area. In the application, the positive electrode sheet, the negative electrode sheet and the diaphragm are pressed together to avoid the winding core from being wound too tightly due to the respective tension, the first composite area can reinforce the bonding between the diaphragm and the negative electrode sheet to prevent relative sliding, and the second composite area can fix the positive electrode sheet at a set position to form a compensation area, that is, a certain gap is left between the positive electrode sheet and the negative electrode sheet in the non-composite area, the gap between the electrode sheets in the winding core arc area is increased, space is reserved for the battery cycle expansion, and the problem of battery cycle expansion deformation is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, and particularly discloses a battery cell assembly and a battery comprising the same. BACKGROUND

[0002] With the development of lithium ion battery technology, the market has higher requirements for the fast charging capability and energy density of batteries. At present, the most effective method to improve the energy density of batteries is to use new materials, such as using high-capacity silicon-based materials as the negative electrode. However, during the use of the wound battery, the silicon-based negative electrode material expands greatly during the cycle, which easily squeezes the positive electrode sheet and causes the bending section of the positive electrode sheet to break. SUMMARY

[0003] The present application aims to solve at least part of the technical problems mentioned above, and the purpose is achieved by the following technical solutions:

[0004] In a first aspect, the present application provides a battery cell assembly, which comprises a first diaphragm, a negative electrode sheet, a second diaphragm and a positive electrode sheet which are sequentially stacked and wound, the battery cell assembly having a flat section and a bending section; along the length direction of the negative electrode sheet, the first diaphragm and the second diaphragm are respectively bonded to the negative electrode sheet and form a first composite area; along the length direction of the positive electrode sheet, the positive electrode sheet and the second diaphragm are bonded at least in part and form at least one bonding part, the positive electrode sheet and the second diaphragm at the position of the bonding part and the negative electrode sheet and the first diaphragm corresponding to the position of the bonding part together form a second composite area; the second composite area is located at the flat section, and along the length direction of the negative electrode sheet, the size of the second composite area is smaller than the size of the first composite area.

[0005] In some embodiments, along the width direction of the battery cell assembly, the distance between the maximum curvature point of the innermost layer of the bending section of the battery cell assembly and the maximum curvature point of the outermost layer of the bending section of the battery cell assembly is R, and along the thickness direction of the battery cell assembly, the thickness of the battery cell assembly is H, satisfying 1.05≤R:(H / 2)≤1.3.

[0006] In some embodiments, along the length direction and / or the width direction of the negative electrode sheet, the first diaphragm and the second diaphragm extend beyond the negative electrode sheet, and the part of the first diaphragm and the second diaphragm extending beyond the negative electrode sheet along the length direction and / or the width direction of the negative electrode sheet are bonded to each other to form a third composite area.

[0007] In some embodiments, at least one second composite area is arranged on the flat section of the innermost layer of the battery cell assembly to the flat section of the fourth outermost layer of the battery cell assembly.

[0008] In some embodiments, the projections of the second composite regions on the flat sections of the adjacent two coil layers of the battery cell assembly do not overlap in the thickness direction of the battery cell assembly; or, the projections of the second composite regions on the flat sections of the adjacent two coil layers of the battery cell assembly partially overlap in the thickness direction of the battery cell assembly.

[0009] In some embodiments, referring to Figure 4 , the sizes of the adjacent two second composite regions increase successively in the winding direction of the battery cell assembly, or the sizes of all the second composite regions are equal.

[0010] In some embodiments, the positive electrode sheet has a positive electrode sheet starting end located at the innermost coil layer of the battery cell assembly, the innermost coil layer has a first positive electrode flat section and a first positive electrode curved section connected to the first positive electrode flat section, the positive electrode sheet starting end is the starting position of the first positive electrode flat section, and the first positive electrode flat section has a first second composite region; in the winding direction of the battery cell assembly, the starting end of the first second composite region is flush with the positive electrode sheet starting end; or, the distance between the starting end of the first second composite region and the positive electrode sheet starting end is D, and 0mm < D≤ 3mm is satisfied; and / or, in the winding direction of the battery cell assembly, the ending end of the first second composite region is located at most at the junction of the first positive electrode flat section and the first positive electrode curved section.

[0011] In some embodiments, the area of a single second composite region is S; the projections of the second composite regions on the flat sections of the adjacent two coil layers of the battery cell assembly at least partially overlap on the negative electrode sheet in the thickness direction of the battery cell assembly, and the overlapping area is S1, satisfying 0.2≤ S1 / S≤ 1.

[0012] In some embodiments, the battery cell assembly further comprises a positive electrode tab connected to the positive electrode sheet and a negative electrode tab connected to the negative electrode sheet, and the positive electrode tab and the negative electrode tab are both arranged on the flat sections of the battery cell assembly; the positive projection of the second composite region and the positive electrode tab arranged on the flat section where the second composite region is located in the thickness direction of the battery cell assembly does not overlap; and / or the positive projection of the second composite region and the negative electrode tab arranged on the flat section where the second composite region is located in the thickness direction of the battery cell assembly does not overlap.

[0013] In some embodiments, the flat section where the positive electrode tab is located has a second composite region, and the distance between the end of the second composite region close to the positive electrode tab and the end of the positive electrode tab close to the second composite region in the width direction of the battery cell assembly satisfies d1≥ 0.5mm; and / or, the flat section where the negative electrode tab is located has a second composite region, and the distance between the end of the second composite region close to the negative electrode tab and the end of the negative electrode tab close to the second composite region in the width direction of the battery cell assembly satisfies d2≥ 0.5mm.

[0014] In some embodiments, the battery cell assembly further comprises a positive tab connected to the positive tab sheet, and the bonding strength between the positive tab and the second separator is F; the bonding strength between the positive tab sheet and the second separator in the second composite region is F2, and F2≥F is satisfied.

[0015] In some embodiments, along the length direction of the negative tab, the distance between the end of the second composite region and the edge of the nearest bending section is D1, and D1≥0.5 mm is satisfied.

[0016] In some embodiments, along the length direction of the negative tab, the size of a single straight section is L, the size of a single second composite region is L1, and 3 mm≤L1≤L is satisfied; and / or, along the width direction of the negative tab, the size of the second composite region is W1, the size of the positive tab sheet is W, and 5 mm≤W1≤W is satisfied.

[0017] In some embodiments, along the length direction of the negative tab, the size of the third composite region near the head or tail end of the negative tab is L2, and 0.5 mm≤L2≤2L is satisfied; and / or, along the width direction of the negative tab, the two sides of the negative tab are respectively provided with a third composite region, and the size of a single-side third composite region along the width direction of the negative tab is W2, and 0.2 mm≤W2≤2 mm is satisfied.

[0018] In some embodiments, the bonding strength between the first or second separator of the first composite region and the negative tab is F1, the bonding strength between the positive tab of the second composite region and the second separator is F2, and the bonding strength between the first separator and the second separator of the third composite region is F3, wherein F2≥F1 is satisfied between F1 and F2; and / or, F3≥F1 is satisfied between F1 and F3; and / or, 1 N / m≤F1≤15 N / m is satisfied; and / or, 1.5 N / m≤F2≤30 N / m is satisfied; and / or, 1 N / m≤F3≤15 N / m is satisfied.

[0019] In some embodiments, the positive tab sheet has a positive active coating layer, the positive active coating layer has a functional structure region, at least part of the functional structure region is located in the bending section, the surface density of the positive active coating layer in the functional structure region is ρ1, the surface density of the positive active coating layer in the straight section is ρ2, and ρ1<ρ2 is satisfied.

[0020] In some embodiments, along the winding direction of the battery cell assembly, functional structure regions are arranged on at least two bending sections connected to the straight section with the positive tab.

[0021] In some embodiments, the bending section where at least part of the functional structure region is located and the straight section where the second composite region is located are located in the same layer of the battery cell assembly.

[0022] In some embodiments, the positive sheet of the functional structure area is provided with a recess; the recess has at least two holes, the depth of the hole is h, the diameter of the hole is d, the distance between adjacent two holes is m, and 0mm≤m≤5mm is satisfied; and / or, 2μm≤h≤80μm is satisfied; and / or, 10μm≤d≤200μm is satisfied; and / or, the recess has at least one groove, the size of the groove along the length direction of the positive sheet is L3, and 2mm≤L3≤12mm is satisfied; and / or, the size of the groove along the width direction of the positive sheet is greater than or equal to 2mm and less than or equal to the width of the positive sheet; and / or, the size of the groove along the thickness direction of the positive sheet is greater than or equal to 2μm and less than or equal to the thickness of the positive sheet.

[0023] In some embodiments, along the length direction of the positive sheet, the size L1 of the single second composite area and the depth h of the hole in the recess satisfy: 1.5≤L1 / h≤20000; and / or, along the length direction of the positive sheet, the size L1 of the single second composite area and the size L3 of the groove in the recess satisfy: 0.3≤L1 / L3≤20.

[0024] In some embodiments, in the battery cell assembly, the thickness of the negative sheet is G, the thickness of the first diaphragm is g1, the thickness of the second diaphragm is g2, the distance between adjacent two layers of positive sheets in the bending section of the battery cell assembly is the positive sheet gap, and the size of at least one positive sheet gap in the bending section is H1, which satisfies: G+g1+g2+5μm≤H1≤G+g1+g2+30μm.

[0025] In a second aspect, the present application provides a battery comprising the battery cell assembly of the first aspect.

[0026] The technical scheme provided by the present application has at least the following technical effects:

[0027] In the present application, the positive sheet, the negative sheet and the diaphragm are pressed together to avoid the winding of the winding core due to the tension of each sheet, thereby increasing the gap between the positive and negative sheets. Specifically, the negative sheet, the first diaphragm and the second diaphragm form a first composite area, which can reinforce the adhesion between the diaphragm and the negative sheet, form a composite sheet with high strength, and is beneficial to the relative sliding between the positive sheet and the diaphragm when the positive sheet and the composite sheet form a second composite area. The second composite area can fix the positive sheet at a set position on the negative sheet, and the positive sheet forms a compensation area, i.e. an un-composite area, between adjacent two second composite areas, thereby increasing the sheet gap in the circular arc area of the winding core, reserving space for battery cycle expansion, and effectively solving the problem of battery cycle expansion deformation. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to better combine the content shown in the drawings of the specification with the content described in the specific embodiments, the drawings of the specification are briefly introduced as follows. It can be understood that the drawings of the specification mentioned below only schematically show the related technical solutions and some embodiments of the technical solutions of the present application, and under the premise of not paying creative labor, the person skilled in the art can also make drawings showing other embodiments.

[0029] Specifically, the annotations of the drawings of the specification are as follows:

[0030] Figure 1 A first cross-sectional view of the electric cell assembly in the laminated state along the length direction of the negative electrode tab according to some embodiments of the present application;

[0031] Figure 2 A cross-sectional view of the electric cell assembly in the laminated state along the width direction of the negative electrode tab according to some embodiments of the present application;

[0032] Figure 3 A second cross-sectional view of the electric cell assembly in the laminated state along the length direction of the negative electrode tab according to some embodiments of the present application;

[0033] Figure 4 A structural schematic view of the first electric cell assembly in the wound state according to some embodiments of the present application;

[0034] Figure 5 A structural schematic view of the second electric cell assembly in the wound state according to some embodiments of the present application;

[0035] Figure 6 A structural schematic view of the third electric cell assembly in the wound state according to some embodiments of the present application;

[0036] Figure 7 A structural schematic view of the electric cell assembly in the wound state according to the comparative example.

[0037] Specifically, the annotations of the drawings of the specification are as follows:

[0038] 100, electric cell assembly; 110, positive electrode tab; 111, positive electrode current collector; 112, positive electrode active coating; 120, negative electrode tab; 121, negative electrode current collector; 122, negative electrode active coating; 130, first separator; 140, second separator; 150, positive electrode tab; 160, negative electrode tab; Q1, first composite region; Q2, second composite region; Q3, third composite region; Q4, functional structure region; A1, flat section; A2, curved section; B, compensation region; X, width direction of the electric cell assembly; Y, length direction of the electric cell assembly; Z, thickness direction of the electric cell assembly. DETAILED DESCRIPTION

[0039] To make the content of the embodiments of the present application more clear, the following will be described with reference to the accompanying drawings of the specification. It can be understood that the following mentioned content is only part of the embodiments of the present application, and all the embodiments are enumerated in detail. Therefore, other embodiments obtained based on the following embodiments are within the protection scope of the present application without creative labor.

[0040] It should be understood that the terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the technical solutions. For example, the terms "one", "a" and "said" used herein to modify a feature do not exclude the possibility that the feature can be plural in other embodiments.

[0041] It should be understood that the terms "comprise", "include" and "have" are open terms, which indicate the presence of the stated features but do not exclude the presence of other features. Similarly, the terms "first", "second" and the like used herein to describe a plurality of features merely indicate that the features are different from each other, and do not imply order or sequence unless the context clearly indicates otherwise.

[0042] It should be understood that the terms "set", "connected", "mounted" should be understood broadly unless the context clearly indicates otherwise, for example, can be fixed connection, can also be detachable connection, or integral connection; can be directly connected, or indirectly connected through a medium. For those skilled in the art, the specific meaning of the above terms in the text can be understood according to the specific circumstances.

[0043] In addition, for the convenience of description, the terms of spatial relative relationship will be used herein to describe the position of one feature relative to another feature, for example, "inner", "outer", "end", "side", "upper", "middle", "lower", "high", "low", "axial", "circumferential", "radial", "horizontal", "vertical", "first direction", "second direction" and the like. It can be understood that the spatial relative relationship between two features should include other specific circumstances other than those shown in the accompanying drawings of the specification.

[0044] The background of the present application is further described below.

[0045] With the development of lithium ion battery technology, the market has put forward higher requirements for the fast charging capability and energy density of the battery. At present, the effective method to improve the energy density of the battery is to use new materials. For example, the negative plate is selected to be a high-capacity silicon-based material, which can store a large amount of lithium ions, thereby providing higher energy density. However, the silicon-based material on the negative plate will undergo a large volume expansion during the lithium extraction reaction in the battery charging and discharging process, thereby causing the negative plate to squeeze the positive plate. In the winding cell, the stress concentration is easily generated in the bending segment area of the cell due to the different stress on the inside and outside of the bending segment area. After the negative plate expands, the stress concentration phenomenon of the bending segment will be further intensified. Further, the positive plate of the inner circle layer of the cell is coated with a positive active coating on both sides along the thickness direction and forms a double-sided area, and the positive plate of the outer circle layer of the cell is coated with a positive active coating on one side along the thickness direction and forms a single-sided area. Understandably, the structural strength of the single-sided area is less than that of the double-sided area. Due to the characteristics of the winding structure, compared with the straight segment, the bending segment has a greater outward expansion extrusion force. The part of the winding cell close to the outer circle is the single-sided area of the positive plate, and due to the characteristics of the winding structure, the closer to the outer circle of the winding cell, the more uneven the stress at the bending segment, the greater the expansion force from the inside to the outside, and the smaller the binding force from the outside to the inside. Therefore, the bending segment of the positive plate in the single-sided area is more prone to breakage under the extrusion of the negative plate, and the positive plate in the outer circle single-sided area has no binding force, thereby easily leading to the fact that the positive plate of the bending segment, especially the positive plate of the bending segment in the outer circle single-sided area, is very prone to breakage after the cycle of the cell, and finally affecting the cycle life and performance of the battery.

[0046] To solve the above problems, the existing solution is to locally process the positive plate of the bending segment of the battery, such as setting multiple micropores, recessed areas, etc. to reduce the positive lithium content of the area, reduce the lithium intercalation amount of the corresponding negative plate coating, thereby alleviating the volume expansion of the negative plate coating. However, due to the large expansion of the silicon-based negative material, this technology still cannot completely solve the problem of battery deformation or even plate fracture caused by volume expansion in the later cycle of the battery.

[0047] Therefore, it is necessary to study a new technology to solve the problem of battery deformation or even plate fracture caused by cycle expansion, so as to manufacture a lithium ion battery with high reliability and high energy density.

[0048] The embodiments of the present application will be described below in conjunction with the drawings of the specification.

[0049] In a first aspect, with reference to Figure 1 and Figure 2The application provides an electric core assembly 100, which comprises a first diaphragm 130, a negative electrode sheet 120, a second diaphragm 140 and a positive electrode sheet 110 which are sequentially stacked and wound, the electric core assembly 100 has a flat section A1 and a curved section A2; along the length direction of the negative electrode sheet 120, the first diaphragm 130 and the second diaphragm 140 are adhered to the negative electrode sheet 120 respectively and form a first composite area Q1; along the length direction of the positive electrode sheet 110, the positive electrode sheet 110 is adhered to the second diaphragm 140 at least in a partial area and forms at least one adhered part, the positive electrode sheet 110 and the second diaphragm 140 at the position of the adhered part and the negative electrode sheet 120 and the first diaphragm 130 corresponding to the position of the adhered part jointly form a second composite area Q2; the second composite area Q2 is located at the flat section A1, and along the length direction of the negative electrode sheet 120, the size of the second composite area Q2 is smaller than the size of the first composite area Q1.

[0050] In the above embodiment, with reference to Figure 3 The positive electrode sheet 110 is pressed together with the negative electrode sheet 120 and the diaphragm, so that the winding core is not wound too tightly due to the tension of each part, thereby increasing the gap between the positive and negative electrode sheets 120. Specifically, the negative electrode sheet 120 forms the first composite area Q1 with the first diaphragm 130 and the second diaphragm 140, the adhesion between the diaphragm and the negative electrode sheet 120 is reinforced, the composite sheet with high strength is formed, and the relative sliding between the positive electrode sheet 110 and the diaphragm when the positive electrode sheet 110 forms the second composite area Q2 with the composite sheet is avoided. The second composite area Q2 can fix the positive electrode sheet 110 at a set position on the negative electrode sheet 120, and the positive electrode sheet 110 forms a compensation area B between two adjacent second composite areas Q2, that is, a certain gap is left between the positive electrode sheet 110 and the negative electrode sheet 120 in the un-composite area, so that the positive electrode sheet 110 has a compensation length, thereby increasing the electrode sheet gap of the winding core curved section A2, reserving space for battery cycle expansion, and effectively solving the problem of battery cycle expansion deformation.

[0051] It should be noted that Figure 1 Only the relative position relationship of each part is used for display, and the compensation area B is not shown, Figure 3 The protrusion of the compensation area B can be clearly seen.

[0052] In addition, in the present application, the extending direction of the laminated positive electrode sheet 110 and the negative electrode sheet 120 is consistent with the length direction thereof; and after the winding to form the battery cell assembly 100, the battery cell assembly 100 has a flat section A1 and a curved section A2, wherein the length direction of the flat section A1 is consistent with the length direction of the negative electrode sheet 120, that is, the width direction X of the battery cell assembly, and the length direction Y of the battery cell assembly is the extending direction of the positive tab 150 or the negative tab 160 on the flat section A1, that is, the width direction of the negative electrode sheet 120. Therefore, it can be understood that the battery cell assembly 100 has two perpendicular length direction, width direction and thickness direction, the thickness direction Z of the battery cell assembly is consistent with the thickness direction of the negative electrode sheet 120 and the positive electrode sheet 110, the width direction X of the battery cell assembly is consistent with the length direction of the negative electrode sheet 120 and the positive electrode sheet 110, and the length direction Y of the battery cell assembly is consistent with the width direction of the negative electrode sheet 120 and the positive electrode sheet 110.

[0053] In some embodiments, referring to Figure 4 , along the width direction X of the battery cell assembly, the distance between the two points of the maximum curvature of the innermost layer of the curved section A2 of the battery cell assembly 100 and the maximum curvature of the outermost layer of the curved section A2 of the battery cell assembly 100 is R, and along the thickness direction Z of the battery cell assembly, the thickness of the battery cell assembly 100 is H, which satisfies 1.05≤R:(H / 2)≤1.3.

[0054] In the above embodiments, the distance between the two points of the maximum curvature of the innermost layer and the maximum curvature of the outermost layer of the curved section A2 of the battery cell assembly 100 can be understood as the distance between the two points of the maximum curvature of the inner side diaphragm of the innermost layer of the battery cell assembly 100 and the outer side positive electrode sheet 110 of the outermost layer of the curved section A2, and H / 2 can be understood as the distance between the diaphragm and the outermost electrode sheet of the battery cell along the thickness direction of the battery cell from the winding center of the battery cell. It should be further explained that the left side and the right side of the width direction of the battery cell both have the curved section A2, and the R value of the left curved section A2 and the right curved section A2 of the battery cell can be the same or different. When the distance R between the two points of the maximum curvature of the innermost layer of the left curved section A2 of the battery cell and the maximum curvature of the outermost layer of the curved section A2 of the battery cell is different, the H / 2 corresponding to one half of the thickness of the battery cell is also different. In a specific embodiment, if R is the distance between the two points of the maximum curvature of the innermost layer of the left curved section A2 of the battery cell and the maximum curvature of the outermost layer of the curved section A2 of the battery cell, then H / 2 corresponds to the distance between the outermost electrode sheet of the battery cell in the flat section A1 region close to the left curved section A2 of the battery cell and the diaphragm of the flat section A1 of the winding center of the battery cell along the thickness direction of the battery cell.

[0055] It can be understood that if the value of R:(H / 2) is too small, it means that the gap between the positive plate 110 and the negative plate 120 at the bending section A2 is too small, which cannot effectively cope with the problem of the cyclic expansion of the negative plate 120; and if the value of R:(H / 2) is too large, it means that the gap between the positive plate 110 and the negative plate 120 at the bending section A2 is too large, which will cause the lithium ions to be slow to separate in the electrolyte and reach the negative plate 120, the transmission path of lithium ion deintercalation is long, the transmission speed is slow, and even the lithium precipitation phenomenon will be caused, resulting in the reduction of battery capacity. Therefore, the value of R:(H / 2) should be moderate, for example, R:(H / 2) can be any one of 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.30 or a range between any two of them.

[0056] In some embodiments, the first separator 130 and the second separator 140 exceed the negative plate 120 along the length direction of the negative plate 120 and / or the width direction of the negative plate 120, and the portions of the first separator 130 and the second separator 140 exceeding the negative plate 120 along the length direction and / or the width direction of the negative plate 120 are bonded to each other to form a third composite area Q3.

[0057] It should be understood that the first separator 130 and the second separator 140 correspond to two sides of the packaging bag and encapsulate the negative plate 120 inside, and the excess edge portion of the first separator 130 and the second separator 140 relative to the negative plate 120 constitutes the third composite area Q3, which further increases the bonding strength of the separator and the negative plate 120.

[0058] In some embodiments, a second composite area Q2 is provided on the flat section A1 of at least the innermost circle layer of the battery cell assembly 100 to the flat section A1 of the fourth-to-last outer circle layer of the battery cell assembly 100.

[0059] It should be noted that the second composite area Q2 must be provided on the starting circle layer or the innermost circle layer of the winding core, and the outermost four circle layers can have no composite area; in addition, in some embodiments, the second composite area Q2 can also be provided on the flat section A1 of the outermost circle layer, the second outermost circle layer and / or the third-to-last outer circle layer of the battery cell assembly 100. It can be understood that in the present application, the winding direction of the battery cell assembly 100 refers to the direction of winding from the inside of the battery cell to the outside, and it can also be understood as the length direction of the positive plate 110 and / or the negative plate 120 (i.e. the extension direction of the positive plate 110 and the negative plate 120 after winding).

[0060] Specifically, along the winding direction of the battery cell assembly 100, the second outer layer is the layer connected to the outermost layer, the third outer layer is the layer connected to the inner side of the second outer layer, and the fourth outer layer is the layer connected to the inner side of the third outer layer.

[0061] In addition, the number of the second composite regions Q2 on the flat section A1 is at least one, that is, multiple second composite regions Q2 can be arranged at intervals on one flat section A1.

[0062] In particular, the above-mentioned scheme is part of the implementation, and if no second composite region Q2 is arranged on one or several flat sections A1 from the innermost layer to the fourth outer layer, it also belongs to the protection scope of the present application.

[0063] In some embodiments, referring to Figure 6 , along the thickness direction Z of the battery cell assembly, the projections of the second composite regions Q2 on the flat sections A1 of the adjacent two layers of the battery cell assembly 100 do not overlap; or, referring to Figure 4 and Figure 5 , along the thickness direction Z of the battery cell assembly, the projections of the second composite regions Q2 on the flat sections A1 of the adjacent two layers of the battery cell assembly 100 partially overlap. In some embodiments, the area of a single second composite region Q2 is S; the projections of the second composite regions Q2 on the flat sections A1 of the adjacent two layers of the battery cell assembly 100 on the negative plate 120 along the thickness direction Z of the battery cell assembly at least partially overlap, and the overlapping area is S1, which satisfies 0.2≤S1 / S≤1.

[0064] It should be noted that the projection here refers to the orthographic projection along the thickness direction of the battery cell assembly 100, which can also be said to be the projection on the projection surface of the negative plate 120 along the thickness direction of the battery cell assembly 100; the projection described in the present application is an orthographic projection.

[0065] In summary, the projections of the second composite regions Q2 on the flat sections A1 of the adjacent two layers can not overlap, partially overlap, or completely overlap, and the above schemes are all better than not arranging the second composite region Q2, and all belong to the protection scope of the present application.

[0066] In some embodiments, referring to Figure 4 , along the winding direction of the battery cell assembly 100, the sizes of the adjacent two second composite regions Q2 increase in turn, or referring to Figure 5 , the sizes of all the second composite regions Q2 are equal.

[0067] In the above embodiments, the lengths of all the second composite regions Q2 gradually increase, or the lengths of all the second composite regions Q2 are the same. It should be explained that the lengths of the bending sections A2 of the core from inside to outside gradually increase during winding. In order to adapt to the lengths of the bending sections A2 and to ensure that the distances between adjacent two second composite regions Q2 are consistent as much as possible, and considering the difficulty of process operation, the lengths of the second composite regions Q2 should gradually increase as much as possible.

[0068] In particular, the application should also protect the following solutions: the lengths of all the second composite regions Q2 as a whole show an increasing trend, wherein the lengths of part of adjacent two second composite regions Q2 are the same; and the length of a latter second composite region Q2 is slightly smaller than the length of a former second composite region Q2 along the winding direction of the core.

[0069] In some embodiments, the positive electrode sheet 110 has a positive electrode sheet starting end located at the innermost coil layer of the core assembly 100, the innermost coil layer has a first positive electrode straight section and a first positive electrode bending section connected to the first positive electrode straight section, the positive electrode sheet starting end is the starting position of the first positive electrode straight section, and the first positive electrode straight section has a first second composite region Q2; along the winding direction of the core assembly 100, the starting end of the first second composite region Q2 is flush with the positive electrode sheet starting end; or the distance between the starting end of the first second composite region Q2 and the positive electrode sheet starting end is D, and 0mm < D≤ 3mm is satisfied; and / or, along the winding direction of the core assembly 100, the ending end of the first second composite region Q2 is located at the farthest from the junction of the first positive electrode straight section and the first positive electrode bending section.

[0070] In the above embodiments, the first second composite region Q2 starts at the positive electrode sheet starting end and ends at the junction of the first straight section and the first bending section of the positive electrode sheet 110; that is, the head of the positive electrode sheet 110 must be compounded with the second separator 140, on the one hand to avoid the head of the positive electrode sheet 110 from being warped and folded when passing through the roller, and on the other hand to fix the head of the positive electrode sheet 110 if the head of the positive electrode sheet 110 is not compounded, the positions of the other second composite regions Q2 will fluctuate or the second composite regions Q2 behind will be stretched by the tension of the head of the positive electrode sheet 110, resulting in failure of the second composite regions Q2 and thus failure to achieve compensation of the bending section A2. In summary, the distance D between the starting end of the first second composite region Q2 and the positive electrode sheet starting end should not be more than 3mm.

[0071] In some embodiments, the battery cell assembly 100 further comprises a positive tab 150 connected with the positive electrode tab 110 and a negative tab 160 connected with the negative electrode tab 120, and the positive tab 150 and the negative tab 160 are arranged on the flat section A1 of the battery cell assembly 100; the second composite region Q2 and the positive tab 150 arranged on the flat section A1 where the second composite region Q2 is located do not overlap in the normal projection of the thickness direction of the battery cell assembly 100; and / or the second composite region Q2 and the negative tab 160 arranged on the flat section A1 where the second composite region Q2 is located do not overlap in the normal projection of the thickness direction of the battery cell assembly 100.

[0072] Specifically, the above embodiments can effectively avoid damaging the positive tab 150 and the negative tab 160 when forming the second composite region Q2, and at the same time avoid the burrs of the positive tab 150 and the negative tab 160 from piercing the diaphragm of the second composite region Q2.

[0073] In some embodiments, the flat section A1 where the positive tab 150 is located has the second composite region Q2, and along the width direction X of the battery cell assembly, the distance between the end of the second composite region Q2 close to the positive tab 150 and the end of the positive tab 150 close to the second composite region Q2 is d1, which satisfies d1≥0.5 mm; and / or, the flat section A1 where the negative tab 160 is located has the second composite region Q2, and along the width direction X of the battery cell assembly, the distance between the end of the second composite region Q2 close to the negative tab 160 and the end of the negative tab 160 close to the second composite region Q2 is d2, which satisfies d2≥0.5 mm.

[0074] In the above embodiments, the distance between the edge of the second composite region Q2 and the edge of the positive tab 150 and the negative tab 160 cannot be too close, otherwise the tabs are easily damaged when the second composite region Q2 is compounded, or the burrs at the tabs are easily pierced through the diaphragm under the action of the compounding roller, causing the second composite region Q2 to fail. Specifically, d1 and d2 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, etc.

[0075] In some embodiments, the battery cell assembly 100 further comprises a positive tab 150 connected with the positive electrode tab 110, and the bonding strength between the positive tab 150 and the second diaphragm 140 is F; the bonding strength between the positive electrode tab 110 and the second diaphragm 140 in the second composite region Q2 is F2, which satisfies F2≥F.

[0076] In the above embodiments, the setting of F2≥F can ensure that the positive electrode tab 110 and the negative electrode tab 120 have sufficient bonding strength with the diaphragm, and at the same time can reduce the welding protrusions on the positive tab 150 due to the excessive bonding strength of the positive tab 150 position when the positive tab 150 is formed at the position corresponding to the second composite region Q2, thereby avoiding scratching or piercing the diaphragm to cause safety problems.

[0077] In some embodiments, along the length direction of the negative tab 120, the distance between the end of the second composite area Q2 and the edge of the closest bending section A2 is D1, and D1≥0.5 mm is satisfied.

[0078] It should be noted that the edge of the bending section A2 refers to the junction of the bending section A2 and the straight section A1.

[0079] In the above embodiments, the second composite area Q2 is required to have a certain distance from the bending section A2, so as to prevent the second composite area Q2 from being located at the bending section A2, and thus the positive tab 110 and the negative tab 120 cannot be tightly attached to each other to increase the gap between the positive tab 110 and the negative tab 120. In addition, the lower limit of D1 is defined in the present embodiments, that is, the second composite area Q2 is required to be far enough from the bending section A2 to ensure the bonding strength of the positive tab 110 and the negative tab 120, otherwise, the winding tension of the bending section A2 is too large, which easily causes the bonding failure of the second composite area Q2.

[0080] In some embodiments, along the length direction of the negative tab 120, the size of a single straight section A1 is L, the size of a single second composite area Q2 is L1, and 3 mm≤L1≤L is satisfied; and / or, along the width direction of the negative tab 120, the size of the second composite area Q2 is W1, and the size of the positive tab 110 is W, and 5 mm≤W1≤W is satisfied.

[0081] In the above embodiments, the length and the width of the second composite area Q2 cannot exceed the length and the width of the straight section A1, and the length and the width of the second composite area Q2 cannot be too small, otherwise the bonding strength will be affected. For example, the length L1 of the second composite area Q2 can be 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, etc., and the width of the second composite area Q2 can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, etc.

[0082] In some embodiments, along the length direction of the negative tab 120, the size of the third composite area Q3 close to the head end or the tail end of the negative tab 120 is L2, and 0.5 mm≤L2≤2L is satisfied; and / or, along the width direction of the negative tab 120, the two sides of the negative tab 120 are respectively provided with the third composite area Q3, and the size of a single third composite area Q3 along the width direction of the negative tab 120 is W2, and 0.2 mm≤W2≤2 mm is satisfied.

[0083] It can be understood that the third composite area Q3 provides key adhesion for the diaphragm and the negative electrode sheet 120 to be integrated into one whole, and limiting the size of the third composite area Q3 can improve the adhesion strength of the third composite area Q3, and the first composite area Q1 cooperates to improve the overall strength of the negative electrode composite sheet, to ensure that the diaphragm and the electrode sheet do not separate when the second composite area Q2 is formed, and to improve the stability of the gap of the bending section A2 after winding.

[0084] In the above embodiments, along the length direction of the negative electrode sheet 120, the size of the diaphragm exceeding the negative electrode head or tail is not more than the length of two straight sections A1, otherwise the third composite area Q3 at this position is too long and is wound outside the winding core, increasing the thickness of the battery cell assembly 100, thereby reducing the energy density of the battery; on the contrary, if the length of the third composite area Q3 at the end is too short, it is difficult to ensure the adhesion strength, and therefore the length L2 of the third composite area Q3 near the head or tail of the negative electrode sheet 120 should be moderate, for example, L2 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, etc.

[0085] Similarly, the width W2 of the third composite area Q3 located at the side of the negative electrode sheet 120 also cannot be too wide, otherwise it will increase the size of the negative electrode sheet 120 in the width direction, that is, the size of the battery cell assembly in the length direction Y, which is not conducive to the improvement of the energy density of the battery; on the contrary, if the width of the third composite area Q3 located at the side of the negative electrode sheet 120 is too narrow, it is difficult to ensure the adhesion strength, and therefore the width W2 of the third composite area Q3 located at one side of the negative electrode sheet 120 in the width direction should be moderate, for example, W2 can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, any one value or a range between any two values.

[0086] In some embodiments, the adhesion strength between the first diaphragm 130 or the second diaphragm 140 and the negative electrode sheet 120 of the first composite area Q1 is F1, the adhesion strength between the positive electrode sheet 110 and the second diaphragm 140 of the second composite area Q2 is F2, and the adhesion strength between the first diaphragm 130 and the second diaphragm 140 of the third composite area Q3 is F3, wherein F2≥F1 is satisfied between F1 and F2; and / or, F3≥F1 is satisfied between F1 and F3; and / or, 1N / m≤F1≤15N / m; and / or, 1.5N / m≤F2≤30N / m; and / or, 1N / m≤F3≤15N / m.

[0087] In the above embodiment, the adhesion strength between the two layers of the separator at the edge of the negative electrode sheet 120 is greater than the adhesion strength between the separator and the negative electrode; and the adhesion strength between the positive electrode sheet 110 and the separator in the second composite region Q2 is greater than the adhesion strength between the negative electrode sheet 120 and the separator, which ensures that the positive electrode sheet 110 will not be separated during winding, and is conducive to the formation of the gap between the positive and negative electrode sheets 120 in the un-composite region between the two adjacent second composite regions Q2, thereby increasing the gap between the positive and negative electrode sheets 120 in the curved section A2 of the winding core.

[0088] In some embodiments, the positive electrode sheet 110 has a positive electrode active coating layer 112, the positive electrode active coating layer 112 has a functional structure region Q4, at least part of the functional structure region Q4 is located in the curved section A2, the areal density of the positive electrode active coating layer 112 in the functional structure region Q4 is ρ1, the areal density of the positive electrode active coating layer 112 in the flat section A1 is ρ2, and ρ1< ρ2 is satisfied.

[0089] In the above embodiment, the areal density of the active coating layer in the functional structure region Q4 is small, and the lithium content is relatively small, thereby reducing the amount of lithium intercalation at the corresponding negative electrode sheet 120 of the positive electrode functional structure region Q4, and reducing the expansion of the negative electrode sheet 120 after the lithium intercalation.

[0090] In some embodiments, along the winding direction of the battery cell assembly 100, at least two curved sections A2 connected with the flat section A1 having the positive electrode tab 150 are provided with the functional structure region Q4.

[0091] Further, in some embodiments, along the winding direction of the battery cell assembly 100 (from inside to outside winding), taking the flat section A1 having the positive electrode tab 150 as a reference, at least the following conditions are satisfied: the two positive electrode sheet 110 curved sections A2 connected with the flat section A1 where the positive electrode tab 150 is located are both provided with the functional structure region Q4, and the positive electrode bending section adjacent to the two positive electrode curved sections A2 connected with the flat section A1 where the positive electrode tab 150 is located is also provided with the functional structure region Q4. In another embodiment, along the width direction of the battery cell, at least two curved sections A2 located outside the two positive electrode curved sections A2 connected with the flat section A1 where the positive electrode tab 150 is located are also provided with the functional structure region Q4; that is, along the winding direction of the battery cell assembly 100, taking the flat section A1 having the positive electrode tab 150 as a reference, at least one curved section A2 inside and three curved sections A2 outside are provided with the functional structure region Q4.

[0092] It should be noted that the flat section A1 where the positive electrode tab 150 is located and the sheet circle layer region connected with the flat section A1 where the positive electrode tab 150 is located have relatively large current density and relatively concentrated charge, and the problem of negative electrode sheet 120 expansion is relatively serious, so the positive electrode curved section A2 in these regions needs to be provided with the functional structure region Q4 to improve the negative electrode expansion and the problem of positive electrode curved section A2 fragmentation caused thereby.

[0093] In some embodiments, the curved section A2 where the at least partial functional structure region Q4 is located and the flat section A1 where the second composite region Q2 is located are located in the same layer of the electric core assembly 100.

[0094] In the above embodiments, the functional structure region Q4 and the second composite region Q2 are located in the same winding layer and can act in conjunction, i.e., reducing the expansion of the electrode sheet while increasing the gap of the curved section A2, thereby avoiding the positive electrode sheet 110 being stretched and broken due to being squeezed in the curved section A2.

[0095] In particular, the second composite region Q2 and the functional structure region Q4 can be designed separately in different winding cores or arranged in combination in the same winding core, and both can solve the problem of the expansion of the negative electrode sheet 120, which all belong to the protection scope of the present application.

[0096] In some embodiments, the positive electrode sheet 110 of the functional structure region Q4 is provided with a recess; the recess has at least two holes, the depth of the hole is h, the diameter of the hole is d, the distance between the adjacent two holes is m, and 0mm≤m≤5mm is satisfied; and / or, 2μm≤h≤80μm; and / or, 10μm≤d≤200μm; and / or, the recess has at least one groove, the size of the groove along the length direction of the positive electrode sheet 110 is L3, and 2mm≤L3≤12mm is satisfied; and / or, the size of the groove along the width direction of the positive electrode sheet 110 is greater than or equal to 2mm and less than or equal to the width of the positive electrode sheet 110; and / or, the size of the groove along the thickness direction of the positive electrode sheet 110 is greater than or equal to 2μm and less than or equal to the thickness of the positive electrode sheet 110.

[0097] It should be noted that by setting the holes and / or grooves on the recess of the positive electrode sheet 110 in the curved section A2, the amount of positive electrode coating active material in the curved section A2 is reduced, the deintercalation of lithium ions is reduced, the wettability of the electrolyte is improved, the amount of lithium intercalation of the negative electrode sheet 120 corresponding to the position is reduced, and the problem of sheet breakage caused by the expansion of the negative electrode sheet 120 after the battery is charged and discharged is improved; at the same time, the holes and grooves on the recess can also release part of the stress received by the curved section A2, and improve the problem of fracture of the positive electrode sheet 110 in the curved section A2 caused by excessive stress during the charging and discharging process.

[0098] Specifically, the recess can be formed on the positive electrode active layer, or on the positive electrode current collector 111, or on both the positive electrode current collector 111 and the positive electrode active layer. The recess can be a through hole formed on the positive electrode sheet 110, or a recess formed on the positive electrode sheet 110 by rolling, and the other side surface of the positive electrode sheet 110 opposite to the recess can be provided with a protrusion corresponding to the recess, or can not have a protrusion.

[0099] In the above embodiments, the size parameters of the hole and the groove on the recess should be moderate, not too large, otherwise it will affect the strength of the positive plate 110, and also not too small, otherwise it is difficult to achieve the effect of improving the expansion of the negative plate 120. Specifically, the distance m between the two hole edges can be any one of 0 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm or a range between any two of them; the hole depth h can be any one of 2 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm or a range between any two of them; the hole diameter d can be any one of 10 μm, 50 μm, 100 μm, 150 μm, 200 μm or a range between any two of them. The length L3 of the groove can be any one of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm or a range between any two of them; in addition, if the width of the positive plate 110 is W, the thickness of the positive plate 110 is G1, the width of the groove is W3, and the depth of the groove is h1, then 2 mm≤W3≤W and / or 2 μm≤h1≤G1 are satisfied.

[0100] In some embodiments, along the length direction of the positive plate 110, the size L1 of the single second composite area Q2 and the depth h of the hole in the recess satisfy: 1.5≤L1 / h≤20000; and / or, along the length direction of the positive plate 110, the size L1 of the single second composite area Q2 and the size L3 of the groove in the recess satisfy: 0.3≤L1 / L3≤20.

[0101] In the above embodiments, when the hole or the groove on the recess is cooperatively arranged with the second composite area Q2, it is necessary to ensure that the effect of improving the broken plate is improved while avoiding overcompensation, so that the bending section A2 cannot perform the lithium extraction reaction, resulting in lithium precipitation in the bending section A2. Therefore, the ratio of the length of the second composite area Q2 to the hole depth L1 / h should be moderate, for example, L1 / h can be any one of 1.5, 10, 100, 1000, 10000, 20000 or a range between any two of them; similarly, the ratio of the length of the second composite area Q2 to the groove length L1 / L3 should also be moderate, for example, L1 / L3 can be any one of 0.3, 1, 5, 10, 15, 20 or a range between any two of them.

[0102] In some embodiments, in the battery cell assembly 100, the thickness of the negative plate 120 is G, the thickness of the first separator 130 is g1, the thickness of the second separator 140 is g2, and the distance between the adjacent two layers of positive plates 110 in the bending section A2 of the battery cell assembly 100 is the positive plate gap, and the size of at least one positive plate gap in the bending section A2 is H1, which satisfies: G+g1+g2+5 μm≤H1≤G+g1+g2+30 μm.

[0103] In the above embodiment, at least one positive electrode tab gap is larger than other positive electrode tab gaps, and the larger positive electrode tab gap H1 needs to satisfy G+g1+g2+5μm≤H1≤G+g1+g2+30μm, where g1 and g2 can be equal. It can be seen that the size variation trend of H' and H1 is consistent, because G, g1 and g2 are all preset values. H' cannot be too small, that is, H1 cannot be too small, otherwise the gap between the positive electrode tab 110 and the negative electrode tab 120 is too small, which cannot effectively cope with the problem of the cyclic expansion of the negative electrode tab 120; and if H' is too large, it means that the gap between the positive electrode tab 110 and the negative electrode tab 120 at the bending section A2 is too large, which will cause the lithium ions to be slow to reach the negative electrode tab 120 in the electrolyte, the negative electrode tab 120 to be less embedded with lithium, and the capacity to be reduced. Therefore, the value of H' should be moderate, for example, H' can be any one of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 15μm, 20μm, 25μm, 30μm or a range between any two of them.

[0104] It can be understood that, since G, g1 and g2 are all preset values, the size variation trend of H' and H1 is consistent. H' cannot be too small, that is, H1 cannot be too small, otherwise the gap between the positive electrode tab 110 and the negative electrode tab 120 is too small, which cannot effectively cope with the problem of the cyclic expansion of the negative electrode tab 120; and if H' is too large, it means that the gap between the positive electrode tab 110 and the negative electrode tab 120 at the bending section A2 is too large, which will cause the lithium ions to be slow to reach the negative electrode tab 120 in the electrolyte, the negative electrode tab 120 to be less embedded with lithium, and the capacity to be reduced. Therefore, the value of H' should be moderate, for example, H' can be any one of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 15μm, 20μm, 25μm, 30μm or a range between any two of them.

[0105] It should be noted that the positive electrode tab gap can be obtained by using a gap test method. Specifically, the CT scan cross section of the core is used, and the brighter color is the positive electrode tab coating, which is white. The distance between the adjacent two positive electrode tab coatings is measured using the CT test software, which is the positive electrode tab gap.

[0106] Specifically, some detailed examples and comparative examples are listed below to illustrate the present application:

[0107] I. Preparation of the battery

[0108] General steps: (1) Preparation of positive electrode tab: mix Li[Ni 0.83 Co 0.06 Mn 0.05 Fe 0.06 O2 ternary material, binder polyvinylidene fluoride, and conductive agent carbon black according to a certain mass percentage, add an appropriate amount of N-methyl pyrrolidone as a solvent, stir uniformly, prepare electrode slurry, uniformly coat the prepared positive electrode slurry on aluminum foil, and perform rolling and slitting to form a positive electrode tab.

[0109] (2) Preparation of negative electrode sheet: Artificial graphite, silicon carbon material, styrene-butadiene rubber and conductive carbon black are mixed evenly in a certain mass ratio, deionized water is added to make negative electrode active coating slurry, the above negative electrode active coating slurry is evenly coated on both sides of copper foil, and after drying and compaction by roller press, negative electrode sheet is obtained.

[0110] (3) Battery preparation: The positive electrode sheet, separator (the two sides of the polyethylene film are borosilicate ceramic layer and polyvinylidene fluoride adhesive layer respectively) and the negative electrode sheet prepared in step (1) are wound together to form a core; after injecting electrolyte, the battery is formed, sorted and tested by OCV to obtain the battery.

[0111] Specifically, regarding Example 1: (refer to) Figure 7 According to existing conventional winding technology, the negative electrode sheet, separator and positive electrode sheet are stacked and wound into a core in sequence, and then the core is hot-pressed, packaged, baked, injected with liquid, formed, degassed and sealed, and capacity tested to produce a battery.

[0112] Comparative Example 2: First, the first separator, the negative electrode sheet, and the second separator are stacked and laminated sequentially (laminarization temperature 80℃, lamination pressure 3500N, lamination speed 200mm / s) to form a negative electrode composite sheet (including the first composite region and the third composite region). Then, the positive electrode sheet and the negative electrode composite sheet are wound together using existing winding technology to form a core. After hot pressing, encapsulation, baking, liquid injection, formation, degassing and sealing, and capacity testing of the core, a battery is produced.

[0113] Example 1: First, the first separator, the prepared negative electrode sheet, and the second separator are stacked sequentially, and then hot-pressed together (composite temperature 80℃, composite pressure 3500N, composite speed 200mm / s) to form a negative electrode composite sheet (including a first composite region and a third composite region); then, the positive electrode sheet and the negative electrode composite sheet are intermittently composited together to form multiple second composite regions (the second composite regions are located in the straight section of the core, composite temperature 80℃, composite pressure 250kg, composite speed 250mm / s), and then wound to prepare a core. The distance D between the starting end of the first second composite region and the starting end of the positive electrode sheet is 3mm; the distance d1 between one end of the positive electrode tab and the end of the positive electrode tab near the second composite region is 0.5mm; the distance d2 between the end of the second composite region near the negative electrode tab and the end of the negative electrode tab near the second composite region is 0.5mm; the distance D1 between the end of the second composite region and the edge of the nearest curved section is 0.5mm. Specifically, the length L1 of a single second composite region is 3 mm, the length L' of the first composite region is 1250 mm, the length L of the straight section is 59 mm, the distance R between the innermost layer with the maximum curvature and the outermost layer with the maximum curvature of the curved section is 2.58 mm, the cell assembly thickness H is 3.97 mm, and the area S of a single second composite region is 270 mm².2 The projection overlapping area S1 of the second composite area on the two adjacent flat sections of the circle layer is 54mm 2 The width W of the positive electrode sheet is 90mm, and the width W1 of the second composite area is 90mm.

[0114] Example 2: The same winding core preparation method as Example 1 was used, wherein L1 was 15mm, R was 2.52mm, H was 3.95mm, and S was 1350mm 2 S1 was 1174.5mm 2 The remaining parameters were consistent with Example 1.

[0115] Example 3: The same winding core preparation method as Example 1 was used, wherein L1 was 55mm, R was 2.11mm, H was 4.01mm, and S was 4950mm 2 S1 was 4950mm 2 The remaining parameters were consistent with Example 1.

[0116] Example 4: The same winding core preparation method as Example 1 was used, wherein R was 2.12mm, H was 3.75mm, W1 was 5mm, and S was 75mm 2 S1 was 65.3mm 2 The remaining parameters were consistent with Example 2.

[0117] Example 5: The same winding core preparation method as Example 1 was used, wherein R was 2.51mm, H was 4.03mm, W1 was 50mm, and S was 70mm 2 S1 was 652.5mm 2 The remaining parameters were consistent with Example 2.

[0118] Example 6: The same winding core preparation method as Example 1 was used, wherein R was 2.43mm, H was 3.99mm, and the remaining parameters were consistent with Example 2.

[0119] Example 7: The active coating area of the positive electrode sheet located on the inner side close to the winding center and the outer side away from the winding center of the curved section was punched (such as laser ablation, chemical etching, and convex roller rolling), and the remaining steps of preparing the winding core were the same as Example 1; wherein the hole depth h was 15μm, the hole diameter d was 100μm, the hole gap m was 180μm, R was 2.48mm, H was 4.02mm, and the remaining parameters were consistent with Example 2, i.e. L1 / h was 1000.

[0120] Example 8: A groove is arranged in the inner side of the bending section of the positive electrode sheet, and the remaining steps of preparing the core are the same as those in Example 1; wherein the groove depth is 20 pm, the groove size L3 along the length direction of the positive electrode sheet is 5 mm, the size along the width direction of the positive electrode sheet is 5 mm, R is 2.45 mm, H is 3.98 mm, and the remaining parameters are consistent with those in Example 2, i.e., L1 / L3 is 3.

[0121] After the core of the above examples is prepared, the finished battery is prepared by packaging, liquid injection, formation, and capacity distribution according to the same technical requirements.

[0122] II. Test conditions

[0123] Randomly, 5 pcs of batteries of each example and comparative example are taken out for charge-discharge cycle test (3C constant current charging to 4.3V, 1.8C constant current charging to 4.4V, 1C constant current constant voltage charging to 4.5V, 0.035C cut-off, and then 0.5C discharging to 3.0V), and the process is monitored by CT to monitor the situation of the electrode sheet fragments in the battery.

[0124] Specifically, “whether broken” in the last column of Table 2 refers to whether the positive electrode sheet of the outermost bending section of the core assembly is broken. It should be understood that in practice, the fracture may occur in the bending section of other layers of the positive electrode sheet in addition to the bending section of the outermost positive electrode sheet, and only whether the positive electrode sheet of the bending section of the outermost circle is broken is taken as an example for description in the following table and analysis.

[0125] Table I

[0126] Item L1 (mm) L' (mm) L1 / L' R (mm) H (mm) R / (H / 2) L (mm) L1 / L Example 1 3 1250 0.0024 2.58 3.97 1.3 59 0.05 Example 2 15 1250 0.012 2.52 3.95 1.28 59 0.25 Example 3 55 1250 0.044 2.11 4.01 1.05 59 0.93 Example 4 15 1250 0.012 2.12 3.75 1.13 59 0.25 Example 5 15 1250 0.012 2.51 4.03 1.25 59 0.25 Example 6 15 1250 0.012 2.43 3.99 1.22 59 0.25 Example 7 15 1250 0.012 2.48 4.02 1.23 59 0.25 Example 8 15 1250 0.012 2.45 3.98 1.23 59 0.25 Comparative Example 1 / 1250 / 2.01 4.03 1.00 59 / Comparative Example 2 / 1250 / 2.04 4.05 1.01 59 /

[0127] Table II

[0128] Item [S(mm 2 )]]> [S1(mm 2 )]]> S1 / S W1 (mm) W (mm) W1 / W Capacity retention rate Thickness expansion rate Whether broken Example 1 270 54 0.2 90 90 1 82.81％ 14.48％ No Example 2 1350 1174.5 0.87 90 90 1 83.86％ 13.38％ No Example 3 4950 4950 1 90 90 1 80.41％ 15.73％ No Example 4 75 65.3 0.87 5 90 0.06 84.06％ 12.85％ No Example 5 750 652.5 0.87 50 90 0.56 81.17％ 13.26％ No Example 6 1350 1174.5 0.87 90 90 1 83.84％ 16.41％ No Example 7 1350 1174.5 0.87 90 90 1 85.08％ 13.15％ No Example 8 1350 1174.5 0.87 90 90 1 85.12％ 12.87％ No Comparative Example 1 / / / / 90 / 75.97％ 18.36％ Yes Comparative Example 2 / / / / 90 / 74.45％ 19.02％ Yes

[0129] According to the experimental results in Table 1 and Table 2, when the first composite region, the third composite region and the second composite region are arranged in the battery cell assembly, the positive plate in the battery cell assembly does not break, and the capacity retention rate is also higher, please refer to Examples 1 to 8. Among them, Examples 7 and 8 not only have the above-mentioned composite regions, but also have functional structure regions, i.e. openings or recesses, arranged in the bending section of the positive plate. According to the data in the table, the positive plate of Examples 7 and 8 does not break, and the capacity retention rate of the battery in these two examples is the highest among all the above-mentioned examples. On the contrary, with reference to Comparative Examples 1 and 2, Comparative Example 1 does not have any composite region in the battery cell assembly, and Comparative Example 2 only has the first composite region and the third composite region, but does not have the second composite region. Specifically, the positive plate in the bending section of the outermost side of the battery cell assembly in Comparative Example 1 breaks at 500 cycles, and the positive plate in the bending section of the outermost side of the battery cell assembly in Comparative Example 2 breaks at 530 cycles. The positive plate in these two examples not only breaks, but also has a low capacity retention rate. Therefore, arranging the above-mentioned composite region, especially the second composite region, in the battery cell assembly can effectively prevent the positive plate from breaking and increase the capacity retention rate of the battery.

[0130] In a second aspect, the present application provides a battery comprising the battery cell assembly of the first aspect.

[0131] Therefore, the battery of the second aspect has at least all the technical effects of the battery cell assembly of the first aspect, and the specific technical effects will not be described here. In addition, the embodiments of the present application only illustrate the structure of the battery of the second aspect related to the improvement points of the present application, but do not mean that it does not have other structures. For example, the battery also includes a shell, a cover plate and the like, and other structures will not be described here.

[0132] In particular, the term "and / or" in the present application should be understood as follows:

[0133] In the first case, the term "and / or" between the first subject and the second subject includes any of the following meanings: (1) only the first subject; (2) only the second subject; and (3) the first subject and the second subject.

[0134] In the second case, the term "and / or" between the last two of three or more items in a list of items, means that at least one of the items in the list of three or more items will be present in the combination. For example, "a first item, a second item, and / or a third item" has the same meaning as "first item, second item, and / or a third item," specifically, it will include at least one of the following combinations: (1) only the first item; (2) only the second item; (3) only the third item; (4) the first item and the second item and not the third item; (5) the first item and the third item and not the second item; (6) the second item and the third item and not the first item; and (7) all three of the first item, the second item, and the third item.

[0135] Finally, the embodiments of the present application described above are intended to be illustrative only and in no way limit the scope of the present application. Those skilled in the art will be able to make modifications and variations therefrom without departing from the scope of the present application.

Claims

1. An electrochemical cell assembly, comprising: The battery cell assembly comprises a first diaphragm, a negative electrode sheet, a second diaphragm and a positive electrode sheet which are sequentially stacked and wound, and has a flat section and a curved section; along the length direction of the negative electrode sheet, the first diaphragm and the second diaphragm are respectively bonded with the negative electrode sheet and form a first composite area; along the length direction of the positive electrode sheet, the positive electrode sheet is bonded with the second diaphragm in at least a partial area and forms at least one bonding part, the positive electrode sheet and the second diaphragm at the position of the bonding part and the negative electrode sheet and the first diaphragm corresponding to the position of the bonding part together form a second composite area; the second composite area is located in the flat section, and along the length direction of the negative electrode sheet, the size of the second composite area is smaller than the size of the first composite area; Along the width direction of the battery cell assembly, the distance between the two points of the maximum curvature of the innermost layer of the curved section to the maximum curvature of the outermost layer is R, and along the thickness direction of the battery cell assembly, the thickness of the battery cell assembly is H, satisfying 1.05≤R:(H / 2)≤1.3; The battery cell assembly further comprises a positive electrode tab connected with the positive electrode sheet and a negative electrode tab connected with the negative electrode sheet, and the positive electrode tab and the negative electrode tab are both arranged in the flat section of the battery cell assembly; the positive projection of the second composite area and the positive electrode tab arranged on the flat section where the second composite area is located in the thickness direction of the battery cell assembly does not overlap; and / or the positive projection of the second composite area and the negative electrode tab arranged on the flat section where the second composite area is located in the thickness direction of the battery cell assembly does not overlap; Along the length direction of the negative electrode sheet, the distance between the end of the second composite area and the edge of the curved section closest to the second composite area is D1, and D1≥0.5mm is satisfied.

2. The cell assembly of claim 1, wherein, Along the length direction of the negative electrode sheet and / or the width direction of the negative electrode sheet, the first diaphragm and the second diaphragm exceed the negative electrode sheet, and the parts of the first diaphragm and the second diaphragm exceeding the negative electrode sheet along the length direction and / or the width direction of the negative electrode sheet are bonded with each other to form a third composite area.

3. The cell assembly of claim 1, wherein, At least one second composite area is arranged on the flat section of the innermost layer of the battery cell assembly to the flat section of the fourth outermost layer of the battery cell assembly.

4. The cell assembly of claim 3, wherein, Along the thickness direction of the battery cell assembly, the projections of the second composite areas on the flat sections of the adjacent two layers of the battery cell assembly do not overlap. Alternatively, along the thickness direction of the battery cell assembly, the projections of the second composite areas on the flat sections of the adjacent two layers of the battery cell assembly partially overlap.

5. The cell assembly of claim 3, wherein, Along the winding direction of the battery cell assembly, the sizes of the adjacent two second composite areas increase in turn, or the sizes of all the second composite areas are equal.

6. The cell assembly of claim 1, wherein, The positive electrode sheet has a positive electrode sheet starting end located in the innermost layer of the battery cell assembly, the innermost layer has a first positive electrode flat section and a first positive electrode curved section connected with the first positive electrode flat section, the positive electrode sheet starting end is the starting position of the first positive electrode flat section, and the first positive electrode flat section has a first second composite area. The starting end of the first second composite region is flush with the starting end of the positive electrode tab along the winding direction of the battery cell assembly; Alternatively, the distance between the starting end of the first second composite region and the starting end of the positive electrode tab is D, and 0 mm < D ≤ 3 mm is satisfied; And / or, the ending end of the first second composite region is located farthest at the junction of the first positive electrode flat section and the first positive electrode curved section along the winding direction of the battery cell assembly.

7. The cell assembly of claim 4, wherein, The area of a single second composite region is S; The second composite region on the flat section of the adjacent two layers of the battery cell assembly at least partially overlaps in the thickness direction of the battery cell assembly on the negative electrode tab, and the overlapping area is S1, satisfying 0.2 ≤ S1 / S ≤ 1.

8. The cell assembly of claim 1, wherein, The flat section where the positive electrode tab is located has the second composite region, and the distance between the end of the second composite region close to the positive electrode tab and the end of the positive electrode tab close to the second composite region along the width direction of the battery cell assembly is d1, satisfying d1 ≥ 0.5 mm; And / or, the flat section where the negative electrode tab is located has the second composite region, and the distance between the end of the second composite region close to the negative electrode tab and the end of the negative electrode tab close to the second composite region along the width direction of the battery cell assembly is d2, and d2 ≥ 0.5 mm is satisfied.

9. The cell assembly of claim 1, wherein, The battery cell assembly further comprises a positive electrode tab connected with the positive electrode tab, and the bonding strength between the positive electrode tab and the second diaphragm is F; The bonding strength between the positive electrode tab and the second diaphragm in the second composite region is F2, satisfying F2 ≥ F.

10. The cell assembly of claim 1, wherein, Along the length direction of the negative electrode tab, the size of a single flat section is L, the size of a single second composite region is L1, and 3 mm ≤ L1 ≤ L is satisfied; And / or, along the width direction of the negative electrode tab, the size of the second composite region is W1, and the size of the positive electrode tab is W, satisfying 5 mm ≤ W1 ≤ W.

11. The cell assembly of claim 2, wherein, Along the length direction of the negative electrode tab, the size of the third composite region close to the starting end or the ending end of the negative electrode tab is L2, and 0.5 mm ≤ L2 ≤ 2L is satisfied; And / or, along the width direction of the negative electrode tab, the two sides of the negative electrode tab are respectively provided with the third composite region, and the size of a single third composite region along the width direction of the negative electrode tab is W2, satisfying 0.2 mm ≤ W2 ≤ 2 mm.

12. The cell assembly of claim 2, wherein, The bonding strength between the first diaphragm or the second diaphragm of the first composite region and the negative electrode tab is F1, the bonding strength between the positive electrode tab of the second composite region and the second diaphragm is F2, and the bonding strength between the first diaphragm and the second diaphragm of the third composite region is F3, wherein F2 ≥ F1 is satisfied between F1 and F2; And / or, F3 ≥ F1 is satisfied between F1 and F3; And / or, 1 N / m ≤ F1 ≤ 15 N / m; And / or, 1.5 N / m ≤ F2 ≤ 30 N / m; And / or, 1 N / m ≤ F3 ≤ 15 N / m.

13. The cell assembly of claim 1, wherein, The positive electrode sheet has a positive electrode active coating layer, at least part of a functional structure region of the positive electrode active coating layer is located in the curved section, the surface density of the positive electrode active coating layer in the functional structure region is ρ1, the surface density of the positive electrode active coating layer in the flat section is ρ2, and ρ1<ρ2 is satisfied.

14. The cell assembly of claim 13, wherein, At least two curved sections connected with the flat section having the positive electrode tab are provided with the functional structure region along the winding direction of the battery cell assembly.

15. The cell assembly of claim 14, wherein, At least part of the functional structure region is located in the curved section and the flat section where the second composite region is located is located in the same layer of the battery cell assembly.

16. The cell assembly of claim 13, wherein, The positive electrode sheet of the functional structure region is provided with a recess; The recess has at least two holes, the depth of the hole is h, the diameter of the hole is d, the distance between adjacent two holes is m, and 0mm≤m≤5mm is satisfied; And / or, 2μm≤h≤80μm; And / or, 10μm≤d≤200μm; And / or, the recess has at least one groove, the size of the groove along the length direction of the positive electrode sheet is L3, and 2mm≤L3≤12mm is satisfied; And / or, the size of the groove along the width direction of the positive electrode sheet is greater than or equal to 2mm and less than or equal to the width of the positive electrode sheet; And / or, the size of the groove along the thickness direction of the positive electrode sheet is greater than or equal to 2μm and less than or equal to the thickness of the positive electrode sheet.

17. The cell assembly of claim 16, wherein, Along the length direction of the positive electrode sheet, the size L1 of a single second composite region and the depth h of the hole in the recess satisfy 1.5≤L1 / h≤20000; And / or, along the length direction of the positive electrode sheet, the size L1 of a single second composite region and the size L3 of the groove in the recess satisfy 0.3≤L1 / L3≤20.

18. The cell assembly of claim 17, wherein, In the battery cell assembly, the thickness of the negative electrode sheet is G, the thickness of the first separator is g1, the thickness of the second separator is g2, the distance between adjacent two layers of positive electrode sheets in the curved section of the battery cell assembly is the positive electrode sheet gap, the size of at least one positive electrode sheet gap in the curved section is H1, and G+g1+g2+5μm≤H1≤G+g1+g2+30μm is satisfied.

19. A battery, characterized by The battery cell assembly comprises any one of claims 1 to 18.

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