A jelly-roll battery and a negative electrode sheet thereof

Abstract

The application discloses a roll core battery and a negative plate thereof. In the roll core battery, the head coil layer of the positive plate comprises a first layer section and a second layer section, the first layer section is located at the winding initial end of the positive plate, and the second layer section is connected with the first layer section and is folded back relative to the first layer section. The negative plate comprises a third layer section located at the winding initial end of the negative plate, and the third layer section is arranged in a laminated mode between the first layer section and the second layer section. The head of the third layer section is provided with a single-sided coating area with a folding structure, the single-sided coating area comprises a first single-sided area and a second single-sided area, and the exposed current collector side surface of the first single-sided area and the exposed current collector side surface of the second single-sided area are arranged in a laminated contact mode. The single-sided coating area with the folding structure can ensure that the head of the negative plate enters the deep folding part of the head coil layer of the positive plate, and can play a good filling role, so that the risk of fracture of the positive plate at the folding part is reduced, and the safety performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a wound cell battery and a negative electrode sheet suitable for the wound cell battery. Background Technology

[0002] Lithium-ion batteries are increasingly used in portable devices, and with the growing intelligence and multifunctionality of these devices, batteries require higher energy densities. In conventional wound batteries, the negative electrode at the innermost ring of the winding structure has a large portion of uncoated active material, thus limiting the improvement of battery energy density. In contrast, wound batteries with interlocking winding structures are attracting increasing attention because the negative electrode at the innermost ring of the winding structure has a double-sided coating structure, allowing the active material on both sides to be utilized.

[0003] However, the insert-type winding structure has significant drawbacks. Please see... Figure 1 In a wound-cell battery with an interlocking structure: the innermost ring of the positive electrode includes a first layer segment 21' and a second layer segment 22' connected to it; the starting end of the winding of the negative electrode is a third layer segment 11' coated with active material on both sides. This third layer segment 11' includes a current collector 11a and active material layers 11b located on both sides of the current collector 11a. This third layer segment 11' is located between the first layer segment 21' and the second layer segment 22'. Because the positive electrode has a high compaction density and is relatively brittle, the head of the negative electrode (i.e., the third layer segment 11') cannot be completely inserted into the bend where the first layer segment 21' and the second layer segment 22' of the positive electrode meet, thus forming a "cavity Q" ( Figure 1 The cavity size L in the cell is greater than zero. This causes the cavity Q to be compressed and form a "sharp corner" during hot pressing. The stress on the positive electrode sheet increases, making it very easy for the sheet to break at the bend. This results in a reduction in battery capacity, and the break also poses a safety risk of puncturing the separator, causing a short circuit or even a fire. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a wound battery and its negative electrode sheet, wherein the single-sided coating area of ​​the folded structure can ensure that the head of the negative electrode sheet is inserted into the bending depth of the head layer of the positive electrode sheet, thereby playing a good filling role, reducing the risk of breakage at the bending point of the positive electrode sheet, and improving the safety performance of the battery.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A wound battery includes a positive electrode and a negative electrode, wherein;

[0007] The head layer of the positive electrode sheet includes a first layer and a second layer. The first layer is located at the initial winding end of the positive electrode sheet, and the second layer is connected to the first layer and folded back relative to the first layer.

[0008] The negative electrode sheet includes a third layer segment located at the initial winding end of the negative electrode sheet, and the third layer segment is stacked between the first layer segment and the second layer segment;

[0009] The head of the third layer is provided with a single-sided coating area with a folded structure. The single-sided coating area includes a first single-sided area and a second single-sided area. The exposed current collector side of the first single-sided area and the exposed current collector side of the second single-sided area are stacked and in contact. The folded position formed at the junction of the first single-sided area and the second single-sided area is located inside the junction of the first layer and the second layer.

[0010] Optionally, in the above-mentioned wound cell, the second single-sided area is connected to the double-sided coating area of ​​the negative electrode sheet, and the X-direction dimension W2 of the second single-sided area is less than or equal to the X-direction dimension W of the head ring of the positive electrode sheet.

[0011] Optionally, in the above-mentioned wound cell, the X-direction dimension W1 of the first single-sided area is less than or equal to the X-direction dimension W of the positive electrode head ring.

[0012] And / or, the X-direction dimension W1 of the first single-sided area is less than, equal to or greater than the X-direction dimension W2 of the second single-sided area.

[0013] Optionally, in the above-mentioned wound cell, the third layer segment further includes a double-sided coated area that is in contact with the second single-sided area.

[0014] Optionally, in the above-mentioned wound battery, the junction of the first single-sided area and the second single-sided area forms a fold-back position, wherein:

[0015] The gap distance between the head end of the first single-sided area away from the fold position and the active coating of the double-sided coating area is greater than or equal to zero.

[0016] Alternatively, the first single-sided area may partially overlap with the double-sided coated area.

[0017] Optionally, the above-mentioned wound cell further includes a filling layer located between the first single-sided region and the second single-sided region.

[0018] Optionally, in the above-mentioned wound cell, the filling layer is a single-layer structure or a multi-layer folded structure.

[0019] Optionally, in the above-mentioned wound battery, the filling layer includes any one or more combinations of adhesive paper, ceramic layer, rubber, and foam.

[0020] Optionally, the above-mentioned wound cell further includes an insulating layer, which is located between the first layer segment and the third layer segment and is connected to the first layer segment;

[0021] The projections of the first single-sided area away from the folded-back end of the single-sided area and the junction of the double-sided coating area of ​​the third layer segment and the second single-sided area on the first layer segment all fall within the area where the insulating layer is located.

[0022] Optionally, in the above-described wound cell, the insulating layer includes a first side and a second side:

[0023] The first side is located between the double-sided coating area of ​​the third layer and the first layer, and the distance M2 between the junction of the double-sided coating area and the second single-sided area and the first side is ≥0.5mm;

[0024] And / or, the second side is located between the first single-sided area and the first layer segment, and the distance M3 between the head end of the single-sided area and the second side is ≥0.5mm.

[0025] Optionally, in the above-mentioned wound battery, the insulating layer includes any one or more combinations of single-sided adhesive paper, double-sided adhesive paper, and ceramic coating.

[0026] Optionally, in the above-mentioned wound battery, a groove is provided on the side of the first layer segment opposite to the insulating layer;

[0027] The projections of the head end of the single-sided region and the junction of the double-sided coating area of ​​the negative electrode sheet and the second single-sided region on the first layer segment all fall within the groove.

[0028] Optionally, in the above-described wound battery, the projection of the groove in the thickness direction of the first layer falls within the projection range of the insulating layer in the same direction.

[0029] Optionally, in the above-mentioned wound battery, in any direction perpendicular to the thickness direction of the first layer, the distance M1 between the side profile of the insulating layer and the groove opening profile is ≥0.1mm.

[0030] Optionally, in the above-mentioned wound cell, the depth D1 of the groove in the electrode thickness direction is not greater than the thickness D of the single-sided active coating of the first layer segment.

[0031] A negative electrode sheet includes a third layer segment located at the initial winding end of the negative electrode sheet. The head of the third layer segment is provided with a single-sided coating area for a stroke folding structure. The single-sided coating area includes a first single-sided area and a second single-sided area. The first single-sided area is used to cover at least part of the exposed current collector side of the second single-sided area by folding back. The junction of the first single-sided area and the second single-sided area is the folding position of the folding structure.

[0032] As can be seen from the above technical solution, in the wound battery and its negative electrode sheet provided by the present invention, the first single-sided area and the second single-sided area at the head of the negative electrode sheet constitute a folded structure. On the one hand, this folded structure can increase the thickness of the head of the negative electrode sheet compared to the single-sided coating area of ​​the single-layer structure, thereby enhancing the filling effect on the inner side of the bend at the connection between the first and second layers of the positive electrode sheet. This helps to prevent the bend at the connection between the first and second layers of the positive electrode sheet from being compressed and forming a "sharp corner" during hot pressing, thus avoiding the problem of breakage at the bend due to excessive bending stress of the positive electrode sheet. On the other hand, since the arc-shaped curved surface at the head of the folded structure (i.e., the folded position at the head of the negative electrode) is similar to the arc-shaped curved surface on the inner side of the bend at the connection between the first and second layers of the positive electrode, it can enhance the filling effect on the inner side of the bend at the connection between the first and second layers of the positive electrode. It also facilitates the complete insertion of the negative electrode head into the deep bend at the connection between the first and second layers of the positive electrode, avoiding the formation of cavities. This helps prevent the formation of "sharp corners" due to pressure in the cavity at the connection between the first and second layers of the positive electrode during hot pressing, which could lead to excessive bending stress and breakage at the bend. Furthermore, by avoiding these "cavities," the energy density of the battery can be improved.

[0033] In short, the wound battery provided by this invention, by setting a single-sided coating area with a folded structure at the head of the negative electrode sheet, can ensure that the head of the negative electrode sheet is inserted into the bending depth of the positive electrode sheet head layer, that is, the head of the negative electrode sheet is closer to the inner side of the bend at the connection between the first and second layers of the positive electrode sheet, avoiding the formation of cavities. This not only helps to prevent lithium plating, but also provides good filling for the bending area of ​​the positive electrode sheet head layer, reducing the curling stress at the bending area of ​​the positive electrode sheet, avoiding the problem of electrode sheet breakage during hot pressing formation, thereby improving the safety performance of the battery. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of a conventional interlocking wound battery, and an enlarged view of the initial winding end of its negative electrode sheet.

[0036] Figure 2 This is a partial structural diagram of a wound battery provided in the first specific embodiment of the present invention.

[0037] Figure 3 for Figure 2A schematic diagram of the folded-back structure of the negative electrode head in the rectangular dashed area (diaphragm omitted).

[0038] Figure 4 for Figure 3 A schematic diagram of the structure of the negative electrode without the head being folded back.

[0039] Figure 5 This is a partial structural diagram of a wound battery provided in a second specific embodiment of the present invention.

[0040] Figure 6 for Figure 5 A schematic diagram of the electrode structure in the rectangular dashed area (diaphragm omitted).

[0041] Figure 7 This is a schematic diagram of the structure of the negative electrode sheet with a filling layer provided in the third specific embodiment of the present invention when the head is not folded back.

[0042] Figure 8 This is a long-term decay data curve of the K value of a wound battery, generated by long-term monitoring, provided as an embodiment of the present invention.

[0043] in:

[0044] 21 / 21' - First segment, 22 / 22' - Second segment

[0045] 11 / 11' - Third layer, 12 / 12' - Fourth layer

[0046] 11a - Current collector, 11b - Active material layer

[0047] Q - cavity, L - cavity size

[0048] 101 - Single-sided coating area, 102 - Double-sided coating area

[0049] 110 - Head end of single-sided area, 111 - First single-sided area, 112 - Second single-sided area, 113 - Fold-back position.

[0050] 114 - Filler layer, 31 - Insulation layer, 210 - Groove, J - Connector area. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] First Specific Embodiment

[0053] The first specific embodiment of the present invention provides a wound cell battery and a negative electrode sheet suitable for the wound cell battery.

[0054] Please see Figure 2 and Figure 3 The first specific embodiment of the present invention provides a wound battery comprising a positive electrode and a negative electrode. Wherein:

[0055] The head layer of the positive electrode sheet includes a first layer segment 21 and a second layer segment 22. The first layer segment 21 is located at the initial winding end of the positive electrode sheet relative to the second layer segment 22. The second layer segment 22 is connected to the first layer segment 21 and folded back relative to the first layer segment 21.

[0056] The head layer of the negative electrode sheet includes a third layer segment 11 and a fourth layer segment 12. The third layer segment 11 is located at the initial winding end of the negative electrode sheet relative to the fourth layer segment 12 and is stacked between the first layer segment 21 and the second layer segment 22. The first layer segment 21 is stacked between the third layer segment 11 and the fourth layer segment 12, thus forming an interlocking structure.

[0057] Furthermore, the head of the third layer segment 11 is provided with a single-sided coating area 101 with a folded structure. Specifically, the single-sided coating area 101 includes a first single-sided area 111 and a second single-sided area 112. The exposed current collector side of the first single-sided area 111 and the exposed current collector side of the second single-sided area 112 are stacked and contact each other. That is, the first single-sided area 111 is flipped 180° relative to the plane where the second single-sided area 112 is located to form a folded structure. The folded position 113 formed at the junction of the first single-sided area 111 and the second single-sided area 112 is located inside the junction of the first layer segment 21 and the second layer segment 22.

[0058] It should be noted that in this article, "electrode head" refers to the inner end of the electrode winding, that is, the initial winding end of the electrode located inside the core, and "electrode head loop" refers to the part of the electrode that is first wound into a loop inside the core (the starting position), which is also the loop where the electrode head is located. Correspondingly, "electrode tail" refers to the outer end of the electrode, that is, the ending winding end of the electrode.

[0059] Furthermore, it should be noted that the “layered setup” mentioned in this article refers to multiple (at least two) sheet-like structures / sides being stacked in a basically parallel manner to form a multi-layered structure.

[0060] In the wound battery provided by this invention, the first single-sided region 111 and the second single-sided region 112 located at the head of the negative electrode sheet constitute a folded structure. On the one hand, this folded structure can increase the thickness of the negative electrode sheet head compared to the single-sided coating area of ​​the single-layer structure, thereby enhancing the filling effect on the inner side of the bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet. This helps to prevent the bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet from forming a "sharp corner" under pressure during hot pressing, thus avoiding the problem of breakage at the bend due to excessive bending stress of the positive electrode sheet. On the other hand, because the folded structure forms an arc-shaped curved head end (i.e., Figure 3 The fold-back position 113 at the right end of the negative electrode sheet is similar to the arc-shaped curved surface structure inside the bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet. This enhances the filling effect on the inside of the bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, and also facilitates the complete insertion of the negative electrode sheet head into the deep bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, avoiding the formation of... Figure 1 The cavity Q in the structure helps to prevent the formation of a "sharp corner" at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode during hot pressing, which would lead to excessive bending stress and breakage of the positive electrode at the bend. Moreover, by avoiding the aforementioned "cavity", the energy density of the battery can be improved.

[0061] In short, the wound battery provided by this invention, by providing a single-sided coating area 101 with a folded structure at the head of the negative electrode sheet, ensures that the head of the negative electrode sheet enters the bending depth of the positive electrode sheet head layer, that is, the head of the negative electrode sheet is closer to the inner side of the bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, thus avoiding the generation of... Figure 1 The cavity Q in the positive electrode not only helps prevent lithium plating, but also effectively fills the bends in the positive electrode head layer, reducing the curling stress at the bends and preventing electrode breakage during hot pressing, thereby improving the battery's safety performance.

[0062] For specific embodiments, please refer to Figures 2 to 4 The second single-sided region 112 is connected to the double-sided coating region 102 of the negative electrode sheet. The double-sided coating region 102 may be part of the third layer segment 11, that is, the third layer segment 11 includes not only the aforementioned single-sided coating region 101, but also the double-sided coating region 102 connected to the second single-sided region 112 in the single-sided coating region 101. Alternatively, in other specific embodiments, the aforementioned double-sided coating region 102 may also be located in the fourth layer segment 12, that is, the third layer segment 11 only includes the aforementioned single-sided coating region 101.

[0063] Specifically, the X-direction dimension W2 of the second single-sided region 112 is less than or equal to the X-direction dimension W of the positive electrode head layer, i.e., 0 < W2 ≤ W; the X-direction dimension W1 of the first single-sided region 111 is less than or equal to the X-direction dimension W of the positive electrode head layer, i.e., 0 < W1 ≤ W. The X-direction dimension W1 of the first single-sided region 111 can be less than, equal to, or greater than the X-direction dimension W2 of the second single-sided region 112, i.e., 0 < W1 ≤ W2, or 0 < W2 ≤ W1.

[0064] Specifically, the gap distance between the head end 110 of the first single-sided area 111, which is away from the fold-back position 113, and the active coating of the double-sided coating area 102 is greater than or equal to zero. That is, the third layer segment 11 includes the double-sided coating area 102 and the single-sided coating area 101. After the head end 110 of the single-sided coating area 101 is folded back, it can be as follows: Figure 3 The active coating shown in the diagram is precisely aligned with the double-sided coating area 102 (i.e., the gap between them is zero; see details). Figure 3 The joint area J in the figure can also maintain a gap distance greater than zero with the active coating of the double-sided coating area 102 (not shown in the figure). Alternatively, in other specific embodiments, the first single-sided area 111 can partially overlap with the double-sided coating area 102, that is, the head end 110 of the single-sided area 101 is folded back and covers the active coating of the double-sided coating area 102. In this case, the X-direction dimension W1 of the first single-sided area 111 is greater than the X-direction dimension W2 of the second single-sided area 112.

[0065] In summary, please refer to Figures 2 to 4 The negative electrode sheet with a novel structure provided in the first specific embodiment of the present invention includes a third layer segment 11 located at the initial end of the negative electrode sheet winding. The head of the third layer segment 11 is provided with a single-sided coating area 101 with a folded structure. The single-sided coating area 101 includes a first single-sided area 111 and a second single-sided area 112. The first single-sided area 111 can cover the exposed current collector side of the second single-sided area 112 by folding back. The junction of the first single-sided area 111 and the second single-sided area 112 forms a folded position 113 of the folded structure.

[0066] It should be noted that, in the wound battery provided by the present invention, in addition to the above-mentioned positive and negative electrode sheets, a separator is also stacked between adjacent positive and negative electrode sheets.

[0067] Second specific embodiment

[0068] Please see Figure 5 and Figure 6 The second embodiment of the present invention provides a wound battery and its negative electrode sheet, which differs from the first embodiment described above only in that: it also includes an insulating layer 31; further, a groove 210 is provided on the side of the first layer segment 21 opposite to the insulating layer 31.

[0069] Specifically, the insulating layer 31 is located between the first layer segment 21 and the third layer segment 11, and is connected to the first layer segment 21. The first single-sided area 111, away from the single-sided area head 110 of the fold-back position 113, and the junction of the double-sided coated area 102 of the third layer segment 11 and the second single-sided area 112, are projected onto the first layer segment 21 in the Z direction (projection direction can be found in [reference]). Figure 5 The middle arrow (Z) falls within the projection range of the insulating layer 31 in the same direction, that is, it falls on the insulating layer 31. For example... Figure 6 As shown, the insulating layer 31 can cover the head 110 of the single-sided region of the first single-sided region 111 near the double-sided coating region 102 of the negative electrode sheet (M3 > zero), and can also cover the position where the double-sided coating region 102 of the negative electrode sheet meets the second single-sided region 112 (M2 > zero). Thus, the insulating layer 31 can ensure the insulation effect at its location, avoiding problems such as increased bending stress during hot pressing of the first layer segment 21 of the positive electrode sheet and puncture of the separator due to uneven surface of the joint area between the double-sided coating region 102 of the negative electrode sheet and the first single-sided region 111.

[0070] Specifically, the insulating layer 31 includes a first side 311 and a second side 312. The first side 311 is located between the double-sided coating area 102 of the third layer segment 11 and the first layer segment 21, with a distance M2 ≥ 0.5 mm between the junction of the double-sided coating area 102 and the second single-sided area 112 and the first side 311; and / or, the second side 312 is located between the first single-sided area 111 and the first layer segment 21, with a distance M3 ≥ 0.5 mm between the end 110 of the single-sided area and the second side 312. The insulating layer 31 effectively maintains good coverage of the junction area between the double-sided coating area 102 and the first single-sided area 111 of the negative electrode sheet.

[0071] In specific implementation, the insulating layer 31 can be any one or a combination of various insulating materials such as single-sided adhesive paper, double-sided adhesive paper, and ceramic coating.

[0072] Furthermore, a groove 210 is provided on the side of the first layer segment 21 opposite to the insulating layer 31. Also, the Z-direction projection (projection direction can be found in the image) on the first layer segment 21 at the single-sided region head end 110 and the junction of the double-sided coating area 102 of the negative electrode sheet and the second single-sided region 112... Figure 5 The arrows Z all fall within the projection range of the groove 210 in the same direction, i.e., within the groove 210. The main functions of the groove 210 are: first, to prevent lithium plating in the area when the "start point" and "end point" of the single-sided coating area 101 of the negative electrode sheet do not overlap; and second, to prevent the area from becoming too thick when the "start point" and "end point" of the single-sided coating area 101 of the negative electrode sheet overlap. In other words, the groove 210 helps to avoid problems such as increased bending stress during hot pressing of the first layer 21 of the positive electrode sheet due to uneven surface of the joint area between the double-sided coating area 102 of the negative electrode sheet and the first single-sided area 111.

[0073] In addition, an insulating layer 31 is provided outside the groove 210 to protect the area, further reducing the risk of lithium plating and short circuits, and improving the safety performance of the battery.

[0074] Specifically, the projection of the groove 210 in the thickness direction of the first layer 21 falls within the projection range of the insulating layer 31 in the same direction. Therefore, the insulating layer 31 can cover the groove 210. Figure 6 As shown, let the X-direction and Y-direction dimensions of the insulating layer 31 be N1 and N3 (not shown in the figure), respectively, and the X-direction and Y-direction dimensions of the groove 210 be N2 and N4 (not shown in the figure), respectively. Then, N1 ≥ N2, N3 ≥ N4. Wherein, the Y-direction dimension of the groove 210 is N4 ≤ N5, where N5 represents the Y-direction dimension of the positive electrode sheet, which is not shown in the figure. The X-direction dimension mentioned in this paragraph refers to the dimension along the length of the electrode sheet before winding; the Y-direction dimension mentioned in this paragraph refers to the dimension along the width of the electrode sheet before winding.

[0075] In a preferred embodiment, in the thickness direction of the first layer segment 21 (see [reference]) Figure 5 In any direction perpendicular to the Z direction shown, the distance M1 between the side profile of the insulating layer 31 and the groove profile of the groove 210 is ≥0.1mm. That is, the side of the insulating layer 31 protrudes radially outward by at least 0.1mm relative to the groove side of the positive electrode 210 to ensure good coverage.

[0076] Specifically, the groove 210 is in the electrode thickness direction (see [reference]). Figure 5 The depth D1 in the Z direction (as shown) is not greater than the thickness D of the single-sided active coating of the first segment 21. See details... Figure 6 Groove 210 is in the electrode thickness direction (see reference). Figure 5 The range of depth D1 in the Z direction (as shown) is: D1≤½(D-D0), where D is the thickness of the first layer segment 21 and D0 is the thickness of the current collector in the first layer segment 21.

[0077] Third specific embodiment

[0078] The third embodiment of the present invention provides a wound cell battery and its negative electrode sheet, which, based on the first or second embodiment described above, further includes a filling layer 114, which helps to avoid the problem of excessive stress and breakage of the negative electrode sheet caused by the formation of a "sharp corner" after the negative electrode sheet is folded back.

[0079] Please see details. Figure 7 The filler layer 114 is located on the inner side of the fold of the single-sided coating area 101, that is, the filler layer 114 is located between the first single-sided area 111 and the second single-sided area 112.

[0080] Specifically, the filling layer 114 can be a single-layer structure or a multi-layer folded structure.

[0081] When the filler layer 114 is a single-layer structure, it can be first pasted to the current collector side of the first single-sided area 111 / second single-sided area 112. When the first single-sided area 111 is folded back relative to the second single-sided area 112, the filler layer 114 is located between the first single-sided area 111 and the second single-sided area 112, which can increase the thickness of the negative electrode head, that is, the thickness of the single-sided coating area folded structure, and further avoid the problem of excessive sheet curling stress at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, which leads to sheet breakage at the bend.

[0082] When the filling layer 114 has a two-layer folded structure, it includes a first filling layer 1141 that adheres to the first single-sided area 111, and a second filling layer 1142 that adheres to the second single-sided area 112. When the first single-sided area 111 folds back relative to the second single-sided area 112, the first filling layer 1141 folds back relative to the second filling layer 1142, thereby forming a two-layer folded filling layer. That is, the crease when the first single-sided area 111 folds back relative to the second single-sided area 112 is located in the area where the filling layer 114 is located, and the filling layer 114 also folds back.

[0083] Alternatively, in other specific embodiments, the filling layer 114 can be set as a multi-layered folded structure with two or more layers according to actual needs, further increasing the thickness of the negative electrode head, that is, the thickness of the folded structure of the single-sided coating area, to avoid the problem of excessive sheet curling stress at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode causing sheet breakage at the bend.

[0084] In practice, the filler layer 114 can be any one or more materials such as adhesive paper, ceramic layer, rubber, and foam.

[0085] The following examples illustrate the use of wound-cell batteries and negative electrode sheets in several specific embodiments. The parameters for each wound-cell battery include: wound cell width (Y-direction dimension) of 59mm, wound cell thickness (Z-direction dimension) of 3.3mm, positive electrode sheet width (Y-direction dimension) of 75mm, innermost ring width (Y-direction dimension) of 55.7mm, positive electrode sheet thickness (Z-direction dimension) of 99µm, positive current collector thickness (Z-direction dimension) of 9µm, and a designed capacity of 3490mAh. Among these:

[0086] (1) In the conventional electrode interlocking structure of the wound battery, both surfaces of the negative electrode current collector are provided with active material layers, and there is no single-sided coating area. After winding, the single-layer length (i.e., the dimension in the X direction) of the innermost ring of the negative electrode is 53 mm. The negative electrode does not penetrate deep into the first bending area of ​​the positive electrode (i.e., the inner depth of the connection between the first layer segment 21 and the second layer segment 22 of the head ring of the positive electrode), leaving a cavity Q with a cavity size L of about 2.7 mm.

[0087] (2) The wound cell provided in the first specific embodiment of the present invention (see also) Figures 2 to 4 A single-sided coating area 101 is provided on the current collector side of the negative electrode sheet. The extension length of the single-sided coating area 101 (i.e., the X-direction dimension of the single-sided coating area 101 in its straight extended state before folding back) is 17 mm (i.e., Figure 4 The sum of the X-direction dimensions of the first single-sided area 111 and the second single-sided area 112 is W1+W2=17mm. After winding, the single-sided coating area 101 of the folded structure (see...) Figure 2 and Figure 3 Located inside the core, the folded-back length is 8.5mm (i.e., the X-direction dimension W1 of the first single-sided area 111 is 8.5mm). After folding back, the head end 110 of the single-sided area of ​​the negative electrode sheet has the same orientation as the first layer segment 21 of the positive electrode sheet located at the innermost part of the core.

[0088] (3) The wound cell battery provided in the third specific embodiment of the present invention (see also...) Figure 7 A filler layer 114, made of adhesive paper, is provided on the inner side of the folded-back area 101 of the negative electrode sheet. After being rolled back, the folded-back position 113 of the single-sided coating area 101 is located in the area covered by the filler layer 114, meaning that the filler layer 114 also folds back. The filler layer 114 mainly provides some support. After the filler layer folds back, it provides some support to the folded-back bend of the single-sided coating area 101 of the negative electrode sheet, preventing the formation of a "sharp corner" after the negative electrode sheet folds back, which would cause excessive stress and lead to the breakage of the negative electrode sheet. It can also increase the folded-back thickness of the single-sided coating area 101 of the negative electrode sheet, which helps to prevent the formation of a "sharp corner" at the folded-back bend of the positive electrode sheet during hot pressing, which would cause excessive stress and lead to the breakage of the negative electrode sheet.

[0089] (4) In the wound battery provided in the second specific embodiment of the present invention, a groove 210 is provided at the position corresponding to the first layer segment 21 of the positive electrode sheet and the head end 110 of the folded single-sided area, and an insulating layer 31 is also provided outside the groove 210 (see See Figure 5 and Figure 6The X-direction dimension N2 of groove 210 is 9 mm, and the Y-direction dimension N4 of groove 210 is the same as the Y-direction dimension N5 of the positive electrode sheet, both being 75 mm. The X-direction dimension N1 of insulating layer 31 is 10 mm, and the Y-direction dimension N3 of insulating layer 31 is 77 mm. The radial outward extension dimension M1 of insulating layer 31 covering the groove opening of groove 210 is 0.5 mm, and the groove depth D1 is 45 μm. The area occupied by groove 210 on the first layer 21 of the positive electrode sheet is formed by completely removing the surface coating on one side of the positive electrode sheet, exposing the positive current collector. After winding, the single-sided end 110 of the third layer of the negative electrode sheet completely falls within the area of ​​groove 210 and insulating layer 31. Furthermore, the measured dimension M2 of the endpoint position from insulating layer 31 to the double-sided coated area 102 of the negative electrode sheet is 1.0 mm. The main functions of the groove 210 are: firstly, to prevent lithium plating in the area where the "start point" and "end point" of the single-sided coating area 101 of the negative electrode sheet do not overlap; and secondly, to prevent the area from becoming excessively thick when the "start point" and "end point" of the single-sided coating area 101 of the negative electrode sheet overlap. Simultaneously, an insulating layer 31 is provided outside the groove 210 to protect this area, further reducing the risk of lithium plating and short circuits, and improving the battery's safety performance.

[0090]

[0091] By comparing the process data in the table above, it was found that the average actual capacity of the cells in the two types of wound batteries with novel negative electrode structures (2) and (3) is basically consistent with the design value. However, the average capacity of the cells in the wound battery with conventional electrode interlocking structure (1) is lower. By conversion, it is basically different from the capacity of the positive electrode in (2) and (3). This shows that the innermost positive electrode in the cells of (1) is severely broken after hot pressing.

[0092] Please see Figure 8 Through long-term monitoring of the K value of the above-mentioned coiled batteries, it was found that the K value of the two coiled batteries with novel negative electrode structures (2) and (3) gradually decreased over time, while the K value of the coiled battery (1) with conventional electrode interlocking structure fluctuated greatly. It was determined that the positive electrode broke during the first fold, resulting in aluminum foil leakage, which caused some aluminum foil to puncture the separator and cause micro short circuit inside the cell, resulting in large long-term K value fluctuation. More seriously, it directly caused a short circuit, making its short circuit ratio higher than that of the novel structure.

[0093] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0094] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0095] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A wound-cell battery, comprising a positive electrode and a negative electrode, characterized in that, The positive electrode sheet includes a first layer segment (21) and a second layer segment (22). The first layer segment (21) is located at the initial winding end of the positive electrode sheet, and the second layer segment (22) is connected to the first layer segment (21) and folded back relative to the first layer segment (21). The negative electrode sheet includes a third layer segment (11) located at the initial end of the negative electrode sheet winding. The third layer segment (11) is stacked between the first layer segment (21) and the second layer segment (22) to form an interlocking winding structure. The head of the third layer (11) is provided with a single-sided coating area (101) with a folded structure. The single-sided coating area (101) includes a first single-sided area (111) and a second single-sided area (112). The junction of the first single-sided area (111) and the second single-sided area (112) forms a folded position (113). The exposed current collector side of the first single-sided area (111) and the exposed current collector side of the second single-sided area (112) are stacked and contacted. The third layer (11) also includes a double-sided coating area (102) connected to the second single-sided area (112), wherein the X-direction dimension W1 of the first single-sided area (111) and the X-direction dimension W2 of the second single-sided area (112) are both smaller than the X-direction dimension of the double-sided coating area (102).

2. The wound-cell battery according to claim 1, characterized in that, The X-direction dimension W2 of the second single-sided region (112) is smaller than the X-direction dimension W of the positive electrode head ring; The X-direction dimension W1 of the first single-sided region (111) is smaller than the X-direction dimension W of the positive electrode head ring; The X-direction dimension W1 of the first single-sided region (111) is less than, equal to or greater than the X-direction dimension W2 of the second single-sided region (112).

3. The wound-cell battery according to claim 1, characterized in that, The gap distance between the head end (110) of the first single-sided area (111) away from the fold position (113) and the active coating of the double-sided coating area (102) is greater than or equal to zero; Alternatively, the first single-sided area (111) may partially overlap with the double-sided coated area (102).

4. The wound-cell battery according to claim 1, characterized in that, It also includes a filling layer (114) located between the first single-sided area (111) and the second single-sided area (112).

5. The wound-cell battery according to claim 4, characterized in that, The filling layer (114) is a single-layer structure or a multi-layer folded structure.

6. The wound-cell battery according to claim 4, characterized in that, The filler layer (114) includes any one or more combinations of adhesive paper, ceramic layer, rubber, and foam.

7. The wound-cell battery according to claim 1, characterized in that, It also includes an insulating layer (31) located between the first layer segment (21) and the third layer segment (11), and connected to the first layer segment (21); The first single-sided area (111) away from the single-sided area head (110) of the folded position (113), and the junction of the double-sided coating area (102) of the third layer segment (11) and the second single-sided area (112), all have their Z-direction projections on the first layer segment (21) falling on the insulating layer (31).

8. The wound-cell battery according to claim 7, characterized in that, The insulating layer (31) includes a first side (311) and a second side (312): The first side (311) is located between the double-sided coating area (102) of the third layer (11) and the first layer (21), and the distance M2 between the junction of the double-sided coating area (102) and the second single-sided area (112) and the first side (311) is ≥0.5mm; And / or, the second side (312) is located between the first single-sided area (111) and the first layer segment (21), and the distance M3 between the head end (110) of the single-sided area and the second side (312) is ≥0.5mm.

9. The wound-cell battery according to claim 7, characterized in that, The insulating layer (31) includes any one or more combinations of single-sided adhesive paper, double-sided adhesive paper, and ceramic coating.

10. The wound-cell battery according to claim 7, characterized in that, The first layer segment (21) has a groove (210) on the side opposite to the insulating layer (31). The Z-direction projection of the single-sided area head end (110) and the junction of the double-sided coating area (102) of the negative electrode sheet and the second single-sided area (112) on the first layer segment (21) both fall within the groove (210).

11. The wound-cell battery according to claim 10, characterized in that, The projection of the groove (210) onto the first layer segment (21) along the Z direction falls within the projection range of the insulating layer (31) in the same direction.

12. The wound-cell battery according to claim 11, characterized in that, In any direction perpendicular to the Z direction of the first layer segment (21), the distance M1 between the side profile of the insulating layer (31) and the groove profile of the groove (210) is ≥0.1mm.

13. The wound-cell battery according to claim 10, characterized in that, The depth D1 of the groove (210) in the Z direction is not greater than the thickness D of the active coating on one side of the first layer (21).

14. A negative electrode sheet for a wound-cell battery as described in any one of claims 1 to 13, characterized in that, The negative electrode includes a third layer (11) located at the initial end of the negative electrode winding. The head of the third layer (11) is provided with a single-sided coating area (101) for forming a folded structure. The single-sided coating area (101) includes a first single-sided area (111) and a second single-sided area (112). The first single-sided area (111) is used to cover at least part of the second single-sided area (112) by folding back so that the exposed current collector side of the first single-sided area (111) and the exposed current collector side of the second single-sided area (112) are stacked and in contact. The junction of the first single-sided area (111) and the second single-sided area (112) is the folded position (113) of the folded structure. The third layer (11) also includes a double-sided coating area (102) connected to the second single-sided area (112), wherein the X-direction dimension W1 of the first single-sided area (111) and the X-direction dimension W2 of the second single-sided area (112) are both smaller than the X-direction dimension of the double-sided coating area (102).

15. The negative electrode sheet according to claim 14, characterized in that, It also includes a filling layer (114) that covers the exposed current collector side of the first single-sided area (111) and / or the second single-sided area (112).

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