Winding core and battery

Abstract

Winding core (100), characterized in that the winding core (100) comprises a first electrode plate (10), a separator (20) and a second electrode plate (30) which are stacked and wound one after the other, the polarities of the first electrode plate (10) and the second electrode plate (30) being opposite; wherein the first electrode plate (10) is provided with a first tab (40), wherein the second electrode plate (30) is provided with a stepped groove (33) arranged opposite the first tab (40), wherein the stepped groove (33) has a first groove (331) and a second groove (332) which are arranged facing away from the first tab (40) and are connected to one another one behind the other, wherein the projection of the second groove (332) is arranged along the thickness direction of the winding core (100) within the projection of the first groove (331); wherein a side of a winding rear end of the first electrode plate (10) facing the second electrode plate (30) has an active layer rear portion and a terminal adhesive tape (60), the head of the terminal adhesive tape (60) covering the active layer rear portion; wherein the orthogonal projection in the thickness direction of the winding core (100), the head of the finishing adhesive tape (60) and the active layer rear portion are all arranged in the second groove (332).

Description

Technical FieldThe present application relates to the field of battery energy technology and, more particularly, to a winding core and a battery.Background ArtWith the rapid development of battery technology, people have placed higher demands on the energy density of the battery, the rapid charging capability, and the charging and discharging rate, and high-performance density rapid charging batteries are also a trend of development of the consumable batteries.In the manufacture of the cores of some batteries, at present, the positive electrode plate, the separator and the negative electrode plate are stacked and then wound from the head to the rear portion with the head of the negative electrode plate as the center.At this time, the difference between the thickness of the tab and the thickness of the paste in the tab center-attachment structure results in a difference in thickness between the tab position and the non-tab position, resulting in a decrease in flatness of the winding core. During molding, uneven pressure may easily occur near the tab, creating a slit in the interfacial bond, which in turn results in lithium precipitation at the tab position and seriously impairs cycle performance and safety of the battery.Content of the Utility ModelOn the basis of this, the present application provides a winding core and a battery to solve the problems of the prior art due to the difference in thickness, such as uneven pressure, slit at the interface, and lithium precipitate at the tab position, which affect the battery performance.The present application provides a winding core including a first electrode plate, a separator, and a second electrode plate stacked and wound one after another, the polarities of the first electrode plate and the second electrode plate being opposite to each other; the first electrode plate is provided with a first tab, the second electrode plate is provided with a step groove disposed opposite to the first tab, the step groove includes a first groove and a second groove disposed facing away from the first tab and connected one after another, the projection of the second groove along the thickness direction of the winding core being disposed within the projection of the first groove; wherein a side of the winding trailing end of the first electrode plate facing the second electrode plate has an active layer rear portion and a finish tape, the head of the finish tape covering the active layer rear portion; wherein the orthogonal projection in the thickness direction of the winding core, the head of the finish tape, and the active layer rear portion are all disposed in the second groove.In one possible embodiment, it is provided that the first electrode plate has a first current collector and a first and a second active layer, which are each arranged on two opposite sides of the first current collector in the thickness direction, wherein, along the winding direction in the active layer rear portion, the rear end of the first active layer is flush with the rear end of the second active layer; or wherein the end of the first active layer exceeds the end of the second active layer; or wherein the end of the second active layer exceeds the end of the first active layer.In one possible embodiment, it is provided that the step groove has a third groove which is arranged facing away from the first groove and is connected to the second groove, wherein the projection of the third groove along the thickness direction of the winding core is arranged within the projection of the second groove, wherein the first step surface of the first groove and the third step surface of the third groove are each on both sides of the second step surface of the second groove; wherein the depth of the first step surface is h1, wherein the depth of the second step surface is h2, wherein the depth of the third step surface is h3, wherein h1, h2 and h3 satisfy the condition 0<h1≤h2≤h3.In one possible embodiment, it is provided that the first electrode plate has a first current collector and first active material layers which are respectively arranged on two opposite sides of the first current collector in the thickness direction, the second electrode plate has a second current collector and second active material layers which are respectively arranged on two opposite sides of the second current collector in the thickness direction; wherein h1 satisfies the condition h1<h3 thickness of the first tab; and / or wherein h2 satisfies the condition h2<h3 2* thickness of the first active material layer; and / or wherein h3 satisfies the condition that h3 is equal to the thickness of the second active material layer.In one possible embodiment, it is provided that h1 erfüllt the condition h1=h3-1 / 2*thickness of the first tab; and / or wherein h2 erfüllt the condition h2=h3-thickness of the first active material layer.In one possible embodiment, it is provided that at the winding rear end of the first electrode plate an end groove is provided, in which the head of the adhesive termination tape is arranged.In one possible embodiment, it is provided that the winding core further comprises a first protective adhesive tape, wherein the first protective adhesive tape is arranged on the first electrode plate, and wherein the first protective adhesive tape covers the first tab, wherein the first protective adhesive tape extends along the winding direction of the winding core and at least partially covers the sheet segment of the winding core on a side which is closest to the first tab.In one possible embodiment, it is provided that the winding core further comprises a second protective adhesive tape, wherein the second protective adhesive tape is arranged on the second electrode plate, and wherein the second protective adhesive tape covers the step groove.In one possible embodiment, it is provided that a gap is formed in the width direction of the second electrode plate between the edge of the step groove and the edge of the second electrode plate.In one possible embodiment, it is provided that the first electrode plate has a first current collector and first active material layers which are respectively arranged on two opposite sides of the first current collector in the thickness direction, wherein a first cutout is formed on the first active material layer; and / or wherein the second electrode plate has a second current collector and second active material layers which are respectively arranged on two opposite sides of the second current collector in the thickness direction, wherein a second cutout is formed on the second active material layer.The present application relates to a battery which has a housing and an abovementioned winding core, the winding core being arranged in the housing.In the winding core and the battery provided in the present application, the winding core is connected to a terminal adhesive tape at the winding rear end of the first electrode plate. In the thickness direction of the winding core, the projection of the connection region between the terminal adhesive tape and the first electrode plate is located in the second groove of the step groove, so that the thickness of the first tab and the first electrode plate at the winding trailing end is accommodated in the step groove, thereby reducing the step change at the active layer rear portion, thereby reducing the difference in thickness between adjacent positions near the tab position, improving the flatness of the winding core, thereby reducing the uneven pressure near the tab during the formation, and avoiding the occurrence of a slit at the interfacial bond, and mitigating the problem of lithium precipitation at the tab position.Brief Description of the FiguresIn order to more clearly explain the technical solutions of the embodiments of the present application or the related art, the drawings required for the descriptions in the embodiments or the related art will be briefly described below. Obviously, the accompanying drawings in the following description are some embodiments of the present application, and other drawings without any creative effort can be derived from these drawings by those skilled in the art. FIG. 1 is a first schematic structural diagram of the winding core provided by an embodiment of the present application. FIG. 2 is a second schematic structural diagram of the winding core provided by an embodiment of the present application. FIG. 3 is a schematic structural illustration at the position of the first tab in the winding core of FIG. 1. FIG. 4 is a schematic structural illustration at the position of the first tab in the winding core of FIG. 2. FIG. 5 is a schematic enlarged structural diagram in part A in FIG. 3. FIG. 6 is a schematic diagram illustrating the respective positional relationship between the first electrode plate and the second electrode plate of the winding core provided by an embodiment of the present application. FIG. 7 is a schematic structural diagram of a winding core of a comparative example.List of reference characters100. Winding core; 10. First electrode plate; 11. First current collector; 12. First active material layer; 121. First tab groove; 123. First Recess; 13th First Active Layer; 14th Second Active Layer; 20th Separator; 30th Second Electrode Plate; 31st Second Current Collector; 32nd Second Active Material Layer; 33th Step Groove; 331. First groove; 332. Second groove; 333. Third groove; 334. First step surface; 335. Second step surface; 336. Third step surface; 34th Second recess; 40th First tab; 50th Second tab; 60th Seal tape; 70th First Protective tape; 200. Arc segment; 300. Straight section.Detailed DescriptionIn order to clarify the purpose of the technical solutions and the advantages of the present application, the technical solutions of the preferred embodiments of the present application will be described in more detail below in conjunction with the drawings of the embodiments of the present application. In the figures, the same or similar reference numerals represent the same or similar components or components having the same or similar functions throughout. The described embodiments are some of the embodiments of this application and not all of the embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and are only for explaining the present application, but should not be construed as limiting the present application. All other embodiments that would be obtained without any creative action by a person of ordinary skill in the art based on the embodiments in the present application are within the scope of the present application. The embodiments of the present application will be described below in detail in conjunction with the accompanying drawings.In describing the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "mounted", "connected", and "connected" are to be understood in the broadest sense, which may be, for example, a fixed connection or an indirect connection via an intermediate medium, and may be the internal connection of two elements or an inter-relation between two elements. Those skilled in the art can understand the specific meanings of the above terms in the present application according to specific situations.In describing the present application, it is to be understood that the orientations or positional relationships indicated by the terms "upper", "lower", "front", "rear", "vertical", "horizontal", "roof", "bottom", "inside", "outside" and the like are the shown orientations or positional relationships based on the drawings and are only for convenience of description of the present application and convenience of description, rather than indicating or implying that said device or element has a particular orientation or orientation or must be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present application.The terms "first", "second", or "third" or the like (if present) in the specification and claims of this application and the above drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence.Moreover, the terms "include" and "have", as well as any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, product, or display comprising a sequence of steps or elements is not necessarily intended to be limited to the expressly listed steps or units, but also to include other steps or elements not expressly listed or inherent to the process, method, product, or display.In the conventional technique, the winding core is currently formed by stacking the positive electrode plate, the separator, and the negative electrode plate on each other and then winding them from the head toward the rear portion, with the head of the negative electrode plate forming the center. In this case, the tab is welded to the corresponding electrode plate through the slot on the tab by means of laser or ultrasonic welding. In the structure of centrally attaching the tab (the tab is disposed in the center of the electrode plate and, after winding, the tab is disposed in the center of the winding core), the thickness of the tab is different from the thickness of the active material paste part on the electrode plate, resulting in a difference in thickness between the tab position and the non-tab position on the electrode plate. After winding to form a winding core, regions of different thickness are arranged on the surface of the winding core, which has an effect on the flatness of the winding core. During formation, uneven pressure may easily occur near the tab position, resulting in a slit at the interfacial bond, resulting in lithium precipitation at the tab position, which impairs cycle performance and safety of the final formed battery.After repeatedly rethinking and checking, the inventor has found that the uneven surface problem of the winding core caused by the difference between the thickness of the electrode plate and the thickness of the paste can be solved when a step groove is provided on the second electrode plate opposite to the first electrode plate so that the winding trailing end of the first electrode plate at the rear portion of the winding core during winding does not protrude beyond the projection area of the first tab and projects into the step groove, thereby reducing the possibility of generation of the slit at the interface and improving the cycle performance of the battery.In view of this, the present invention provides a winding core including a first electrode plate, a separator, and a second electrode plate stacked and wound one after another, the polarities of the first electrode plate and the second electrode plate being opposite to each other; the first electrode plate is provided with a first tab, the second electrode plate is provided with a step groove disposed opposite to the first tab, the step groove includes a first groove and a second groove disposed facing away from the first tab and connected one after another, the projection of the second groove along the thickness direction of the winding core being disposed within the projection of the first groove; wherein a side of the winding rear end of the first electrode plate facing the second electrode plate has an active layer rear portion and a finishing tape, wherein the head of the finishing tape covers the active layer rear portion; wherein the orthogonal projection of the finishing tape in the thickness direction of the winding core, the head of the finishing tape and the active layer rear portion are all arranged in the second groove.The winding core is connected to a terminating adhesive tape at the winding rear end of the first electrode plate. In the thickness direction of the winding core, the orthogonal projection of the connection region between the terminal adhesive tape and the first electrode plate is located in the second groove of the step groove, so that the thickness of the first tab and the first electrode plate at the winding rear end is accommodated in the step groove, thereby reducing the step change at the active layer rear portion, thereby reducing the thickness difference between adjacent positions near the tab position, improving the flatness of the winding core, thereby reducing the uneven pressure near the tab during the formation, avoiding the occurrence of the slit at the interfacial bond, and mitigating the problem of lithium precipitation at the tab position.The contents of the present invention will be described in detail below in conjunction with the accompanying drawings in order that those skilled in the art may understand the contents of the present invention more clearly and in more detail.FIG. 1 is a first schematic structural diagram of the winding core provided by an embodiment of the present application, FIG. 2 is a second schematic structural diagram of the winding core provided by an embodiment of the present application, FIG. 3 is a schematic structural diagram at the position of the first tab in the winding core of FIG. 1, FIG. 4 is a schematic structural diagram at the position of the first tab in the winding core of FIG. 2.As shown in FIGS. 1 to 4, the embodiments of the present application provide a winding core 100 including a first electrode plate 10, a separator 20, and a second electrode plate 30 that are sequentially stacked and wound. The first electrode plate 10 and the second electrode plate 30 have opposite polarities, and the separator 20 is disposed between the adjacent first electrode plate 10 and the second electrode plate 30 to prevent contact short-circuiting between the first electrode plate 10 and the second electrode plate 30.As shown in FIG. 1, the winding core 100 is provided with a sheet segment 200. It is to be understood that the arc segment 200 is the region where the first electrode plate 10, the separator 20, and the second electrode plate 30 are bent when being wound. For example, as shown in FIG. 1, both ends of the winding core 100 in the left-right direction are arc segments 200. Optionally, the winding core 100 further comprises a straight portion 300 connected to the sheet segment 200.The winding core 100 further comprises a first tab 40, a second tab 50 and a final adhesive tape 60. The first tab 40 is disposed on the first electrode plate 10, and the second tab 50 is disposed on the second electrode plate 30. The winding rear end of the first electrode plate 10 has an active layer rear portion on a side facing the second electrode plate 20. The terminal adhesive tape 60 is bonded to the winding rear end of the first electrode plate 10, and the head of the terminal adhesive tape 60 covers the active layer rear portion. In the thickness direction, i.e., in the X direction in FIG. 1, of the winding core 100, the orthogonal projection of the connection region between the terminal adhesive tape 60 and the active layer rear portion of the first electrode plate 10 relative to the first tab 40 is away from the sheet segment 200 of the winding core 100 on a side closest to the first tab 40, that is, is disposed on the first tab 40 away from the sheet segment 200 side of the winding core 100 on a side closest to the first tab 40, so that the rear end of the winding core 100 does not exceed the position of the first tab 40.The projection of the winding rear end of the first electrode plate 10 falls on the tab position, whereby the difference in thickness caused by the reduction of the first tab 10 at the rear position of the winding core 100 can be reduced and the flatness of the winding core 100 can be improved.Preferably, the trailing end of the first tab 10 on the surface of the winding core 100 does not protrude beyond the position of the first tab 40 so that the difference in thickness between adjacent positions is ≤40 μm, whereby the uneven pressure on the first tab 40 during forming can be reduced and the occurrence of slit at the boundary surface can be reduced.As shown in FIG. 5, the first electrode plate 10 includes a first current collector 11 and two first active material layers 12, and the two first active material layers 12 are respectively disposed on opposite sides of the first current collector 11 in the thickness direction, a first tab groove 121 is provided on the first active material layer 12, the bottom wall of the first tab groove 121 is a first current collector 11, and the periphery is the first active material layer 12, the first tab groove 121 is provided with a first tab 40 electrically connected to the first current collector 11.In one possible embodiment, it is provided that the two first active material layers 12 are each a first active layer 13 and a second active layer 14, wherein along the thickness direction of the winding core in the active layer rear portion of the first electrode plate 10, the projection of the rear end of the first active layer 13 coincides with the projection of the rear end of the second active layer 14, that is, along the winding direction, the rear end of the first active layer 13 is flush with the rear end of the second active layer 14, as shown in FIG. 2 ; or the length of the projection of the rear end of the first active layer 13 is greater than the length of the projection of the rear end of the second active layer 14, as shown in FIG. 1 ; or the length of the projection of the trailing end of the first active layer 13 is smaller than the length of the projection of the trailing end of the second active layer 14; that is, along the winding direction, the trailing end of the first active layer 13 protrudes beyond the trailing end of the second active layer 14; or the trailing end of the second active layer 14 protrudes beyond the trailing end of the first active layer 13.The first electrode plate 10 has a double-sided region, a single-sided region, and a hollow film region. The double-sided region is a region where the first active material layer 12 is present on both sides of the first current collector 11. The single-sided region is a region in which the first active material layer 12 is present only on one side of the first current collector 11. The hollow film region is a region where only the first current collector 11 is present. Here, on the first electrode plate 10, the double-sided region, the single-sided region and the hollow film region are connected in series, so that the rear portion of the first electrode plate 10 terminates with the hollow film region. The rear portion of the adhesive tape 60 covers the hollow film area.The second electrode plate 30 includes a second current collector 31 and two second active material layers 32, and the two second active material layers 32 are respectively disposed on opposite sides of the second current collector 31 in the thickness direction, and a second tab groove is provided on the second active material layer 32, the bottom wall of the second tab groove is the second current collector 31, and the periphery is the second active material layer 32, and a second tab 50 electrically connected to the second current collector 31 is disposed in the second tab groove.For example, the first electrode plate 10 may be a positive electrode plate and the second electrode plate 30 may be a negative electrode plate; alternatively, the first electrode plate 10 may be a negative electrode plate and the second electrode plate 30 may be a positive electrode plate, but this is not a limitation. When the first electrode plate 10 is a positive electrode plate and the second electrode plate 30 is a negative electrode plate, aluminum foil may be used as the first current collector 11 and copper foil may be used as the second current collector 31.As shown in FIGS. 3 to 5, in one possible embodiment, a step groove 33 is provided on the second electrode plate 30. The step groove 33 is disposed opposite to the first tab 40. The stepped groove 33 has a first groove 331 and a second groove 332, which are arranged facing away from the first tab 40 and are connected to one another one behind the other. Along the thickness direction of the winding core 100, the projection of the second groove 332 is disposed within the projection of the first groove 331.The orthogonal projection in the thickness direction of the winding core 100, the head of the seal tape 60, and the active layer rear portion are all disposed in the second groove 332.By adjusting the depth of various steps of the step groove 33, the difference in thickness on the first tab 40 caused by the reduction in the number of layers of the first tab 40, the tab adhesive, and the rear portion of the first electrode plate 10 as well as the terminal adhesive tape 60 can be further reduced to increase the flatness of the winding core 100.Preferably, the step groove 33 is disposed between the first tab 40 and the rear end of the first electrode plate 10 in the thickness direction of the winding core 100, thereby more evenly stacking the electrode plates on the side opposite to the rear end of the winding core 100, thereby reducing the variation in flatness caused by the opening of the holes and grooves in the thickness direction of the winding core 100. On the other hand, the total thickness of the winding core 100 can be reduced after the thickness of the first tab 40 is accommodated in the step groove 33, so that the space efficiency of the winding core 100 is improved and the energy density is increased.It is preferably provided that the step groove 33 is formed on the second active material layer 32 adjacent to the first tab 40 so that the first tab 40 that affects the flatness of the winding core 100 abuts on the groove, which improves the capacity of the step groove 33, accommodates the thickness of the first tab 40, reduces the total thickness of the winding core 100, and suppresses the variation in flatness caused by the provision of the first tab 40 in the thickness direction.As shown in FIG. 5, the step groove 33 has a third groove 333 disposed away from the first groove 331 and communicating with the second groove 332. Along the thickness direction of the winding core 100, the projection of the third groove 333 is arranged within the projection of the second groove 332. The first step surface 334 of the first groove 331 and the third step surface 336 of the third groove 333 are respectively disposed on both sides of the second step surface 335 of the second groove 332. Along the longitudinal direction of the second electrode plate 30, the sum of the widths of the first step surface 334, the second step surface 335, and the third step surface 336 corresponds to the width of the first tab 40.As shown in FIG. 3, the width L 1 of the first step surface 334 is the distance between the projection position of a side of the first tab 40 facing the wound core arc segment 200 and the projection position of the active layer rear portion adjacent thereto in the thickness direction of the wound core 100.The width L 2 of the second step surface 335 is the distance between the projection position of the rear end of the first active layer 13 and the projection position of the rear end of the second active layer 14 in the thickness direction of the winding core 100; that is, the offset distance when applying the pastes to the end of the inner and outer sides, and a manufacturing margin of ±1 mm is provided.The width L 3 of the third step surface 336 is the distance between the projection position of a side of the first tab 40 facing away from the winding core arc segment 200 and the projection position of another active layer rear portion in the thickness direction of the winding core 100.The connection area between the termination adhesive tape 60 and the active layer rear portion of the first electrode plate 10 is thicker than other areas of the end of the first electrode plate 10 due to the additional termination adhesive tape 60, the projection of the second step surface 335 coincides with it, so that the increased thickness part can be accommodated in the second step surface 335, thereby improving the flatness of this position and further reducing the overall thickness of the winding core 100, so that the space efficiency of the winding core 100 is improved and the energy density is increased.For example, due to variations in the manufacturing process in the width L 1 of the first step surface 334, the width L 2 of the second step surface 335, and the width L 3 of the third step surface 336, the error may increase by 2 mm to 5 mm based on the above dimensions.In one possible embodiment, it is provided that the depth of the first step surface 334 is h1, the depth of the second step surface 335 is h2, the depth of the third step surface 336 is h3, h1, h2and h3being satisfied the condition 0<h1≤h2≤h3.In the thickness direction of the winding core 100, the second step surface 335 and the third step surface 336 have the first tab 40, the rear end of the first electrode plate 10, and the starting end of the terminal adhesive tape 60, so that the thickness here is larger than in other ranges, where h1, h2, and h3 are set to 0<h1≤h2≤h3, whereby the accommodation capacity of the second step surface 335 and the third step surface 336 in the thickness direction can be improved, so that the thickness of the winding core 100 at the position of the step groove 33 is reduced and the thickness variation is reduced, whereby the flatness of the winding core 100 at the position of the step groove 33 is improved.As shown in FIGS. 1 and 2, the winding core 100 further includes a first protective adhesive tape 70. The first protective adhesive tape 70 is disposed on the first electrode plate 10. The first protective adhesive tape 70 covers the first tab 40.For example, referring to FIGS. 3 to 5, on the straight portion 300, the position at which the first protective tape 70 is removed from the arc segment 200 relative to the first tab 40 and the position at which the projection of the rear end of the first active layer 13 overlaps with the projection of the rear end of the second active layer 14 are defined as position a; the position at which the first tab 40 is not disposed in the first tab groove 121 and overlaps with the projection of the finishing tape 60 is defined as position b; the position of the third step surface 336 is defined as position c; the position of the second step surface 335 is defined as position d; the position of the second step surface 335 that overlaps with the end of the outer active layer rear portion (the rear portion of the active material layer that is relatively close to the arc segment 200 adjacent to the first tab 40) is defined as position e; the position of the first step surface 334 is defined as position f; the position where no first tab 40 is attached and that is located opposite to the first tab 40 away from the position b in the first tab groove 121 is defined as position g; the position where the projection of the seal tape 60 overlaps with the double-sided area on a side of the first tab groove 121 facing the arc segment 200 is defined as position h.The depth h 1 of the first step surface 334 is a thickness step that compensates for the position e and the position g. Therefore, 0<h 1<h 3 thickness difference between the position e and the position g.Since the difference in thickness between the position e and the position g is substantially equal to the thickness of the first tab 40, the depth h 1 of the first step surface 334 satisfies the condition 0<h 1<h 3 thickness of the first tab 40.The depth h 2 of the second step surface 335 is a thickness step that compensates the position c and the position g. Therefore, 0<h 1<h 3 thickness difference between the position c and the position g.Since the difference in thickness between the position c and the position g is about twice the thickness of the first active material layer 12, the depth h 2 of the second step surface 335 satisfies the condition h 2<h 3- 2*thickness of the first active material layer 12.The depth h 3 of the third step surface 336 satisfies the condition that h 3 is equal to the thickness of the second active material layer 32, that is, the third step surface 336 has the second current collector 31 as a bottom wall.Preferably, h1 satisfies the condition h1=h3-1 / 2 of the thickness of the first tab 40.Preferably, h2 satisfies the condition h2=h3 thickness of the first active material layer 12.For example, due to variations in the manufacturing process, the depth h 1 of the first step surface 334, the depth h 2 of the second step surface 335, and the depth h 3 of the third step surface 336 may have an error of ±10% based on the above dimensions.In one possible embodiment, it is provided that the winding rear end of the first electrode plate 10 is provided with an end groove. The head of the end adhesive tape 60 is disposed in the end groove.Specifically, the end groove is provided at the rear end of the first active material layer 12.By the arrangement of the end groove, the thickness of the joint portion between the terminal adhesive tape 60 and the first electrode plate 10 is reduced, thereby reducing the variation in thickness of the first electrode plate 10 in the vicinity of the rear position, reducing the difference in thickness at the rear end of the first electrode plate 10 due to the reduction in the number of layers, and improving the flatness of the winding core 100.It is preferably provided that the depth of the end groove is greater than or equal to the thickness of the terminal adhesive tape 60 so that the thickness of the joint region between the terminal adhesive tape 60 and the first electrode plate 10 is not greater than the thickness of the first electrode plate 10 in the vicinity of the rear portion, so that the change in the thickness of the first electrode plate 10 at the rear portion gradually decreases without suddenly increasing.In one possible embodiment, as shown in FIG. 1, it is provided that the first protective adhesive tape 70 extends along the winding direction of the winding core 100 and at least partially covers the sheet segment 200 of the winding core 100 on a side which is closest to the first tab 40.The first protective adhesive tape 70 covers the sheet segment 200 and can increase the thickness of the sheet segment 200 as compared with the straight portion 300, so that during the hot pressing operation of the winding core 100, the sheet segment 200 is subjected to a force and then the interfacial connection becomes stronger, thereby solving the problem of poor adhesion between the separator 20 on the sheet segment 200 and the positive and negative electrodes and improving the long-term cycle performance of the battery.In one possible embodiment, it is provided that the winding core 100 further comprises a second protective adhesive tape, wherein the second protective adhesive tape is arranged on the second electrode plate 30, and wherein the second protective adhesive tape covers the step groove 33.In one possible embodiment, as shown in FIG. 4, it is provided that a gap is formed in the width direction of the second electrode plate 30 between the edge of the step groove 33 and the edge of the second electrode plate 30 adjoining the first tab 40, that is, the second active material layer 32 is arranged between the step groove 33 and the edge of the second electrode plate 30. The width of the gap is A in the width direction of the second electrode plate 30.The negative electrode plate of a conventional lithium ion battery is wider than the positive electrode plate, that is, there is an overhang in the width direction, this difference in width is denoted by B. By disposing the gap, the second active material layer 32 and the first tab 40 can be closely adhered to each other at the gap to prevent the interfacial gap from becoming too large, and to reduce the problem of lithium precipitation in the tab and improve the heat conduction efficiency on the electrode plate.It is preferably provided that A ≥ B so that the contact between the electrode plates at this location becomes wider and the connection narrower.In one possible embodiment, it is provided that the first active material layer 12 is provided with a plurality of first recesses 123. The first recess 123 may be a groove or a strip groove.The groove is a through hole, a blind hole or a counterbore hole on the first electrode plate 10.The recess on the positive electrode plate may chip out some active materials and increase the CB value (cell balance) at the corresponding position, and the hole structure may also store electrolyte, improve the wetting performance of the electrolyte on the electrode plate, and further improve the phenomenon of lithium precipitation.It is preferably provided that the first recess 123 is a hole that may be attached to the edge of the first electrode plate 10, the sheet segment 200, the edge of the first tab 40, the edge of the terminal adhesive tape 60, the edge of the first protective adhesive tape 70, or on the entire surface of the first electrode plate 10, whereby the CB value at the corresponding position can be increased, and the phenomena such as the lithium precipitation at the edge, the lithium precipitation at the sheet, and the lithium precipitation at the tab position on the winding core 100 can be improved.The stripe groove may be formed on the first electrode plate 10 by laser marking.In one possible embodiment, it is provided that the second active material layer 32 is provided with a plurality of second recesses 34.The second recess 34 provided on the negative electrode plate can increase the lithium insertion speed at the corresponding position, improve the dynamics at the negative electrode, and then increase the surface density of the negative electrode, thereby improving the overall energy density of the battery and mitigating the problem of lithium precipitation. Moreover, the liquid storage capacity can also be increased thereby.The second recess 34 may be a second hole formed on the second electrode plate 30 or a groove formed on the first active material layer 12.As shown in FIG. 7, a schematic structural diagram of a winding core of a comparative example of the prior art is shown.The difference between the comparative example and the embodiment of the present application is that in the comparative example, no groove is disposed on the second electrode plate 30 corresponding to the welding region of the first tab 40, and the first active material layer 12 at the rear end of the first electrode plate 10 of the winding core exceeds the first tab 40 and is closer to the arc segment 200 on a side closest to the first tab 40.As shown below, there is a table in which the thickness data of the embodiments of the present application and the comparative examples are compared. The position in the comparative example and the position in the embodiments of the present application are the same with respect to the first tab 40. Here, w is the total thickness of other portions of the winding core, and the span value is the difference in thickness between adjacent positions.As compared with the results of the embodiments, it is seen that by providing the step groove 33, the span value between adjacent positions in the tab region (position b - position h) can be reduced from a maximum of 170 μm to a maximum of 84 μm in the comparative example and reduced to less than 100 μm. In particular, the span value between the position c and the position g is significantly reduced, which improves the interfacial adhesion force in the tab region. Moreover, the thickness variation at each position also becomes smaller, that is, it is flatter, therefore, during forming, the pressure in the vicinity of the tab is more uniform and the likelihood of a slit in interfacial bonding is reduced, thereby mitigating the problem of lithium precipitation at the tab position.Here, the battery is not limited to lithium batteries, and this technology could be applied to sodium batteries in the future. In the embodiments of the present application, lithium ion batteries are preferred.Embodiments of the present application also provide a battery including a battery case and a winding core 100. The winding core 100 is arranged in the battery housing.The specific structure, the functional principle and the function of the winding core 100 have already been described in detail in the above exemplary embodiments and are not repeated here. Note that the manufacturing process of lithium ion batteries is as follows:First step: Preparation of positive electrode plate: Slurry of active layer on positive electrode is prepared, slurry of positive electrode active material is applied to the surface of current collector, and after baking and rolling, first electrode plate 10 is obtained, first electrode plate 10 having a thickness of 70 μm, first electrode plate 10 having a first tab groove 121 having a fixed size at a certain position, and a first tab 40 having a thickness of 100 μm is welded into first tab groove 121 by laser or ultrasonic welding. In the first tab groove 121, a first protective adhesive tape 70 having a thickness of 12 μm is bonded on each side of the electrode plate.Second step: A slurry for the negative electrode active layer is prepared, and the slurry of the negative electrode is applied to a carbon-coated copper foil, and then baked and rolled to obtain a second electrode plate 30, wherein the thickness of the second electrode plate 30 is 105 μm. At a predetermined position of the second electrode plate 30, a second tab groove having a fixed size is provided, the second tab 50 is welded into the slit by laser or ultrasonic welding, and an adhesive tape having a thickness of 12 μm is stuck on both sides of the electrode plate of the second tab groove, respectively. In addition, a step groove 33 is cleaned out of the second electrode plate 30 corresponding to the welding area of the first tab 40. The first step surface 334 has a width of 3 mm and a depth of 30 μm, and the second step surface 335 has a width of 3 mm and a depth of 45 μm, the third step surface 336 has a width of 3 mm and a depth of 50 μm, and the copper foil is visible to the naked eye.Third step: the positive electrode plate and negative electrode plate are cut, cut into disks, and wound with the separator to obtain a winding core. The paste at the rear portion of the positive electrode of the reel core is mapped onto the first tab 40. The width of the terminal adhesive tape 60 covering the positive electrode paste is 3 mm, and the distance between the terminal adhesive tape 60 and the left and right sides of the first tab groove 121 is 3.5 mm.Fourth step: After packaging, baking, liquid filling, forming, secondary sealing, sorting and OCV (open circuit voltage) test, a lithium ion battery is obtained.The electrolyte is a conventional commercial electrolyte and the lithium salt is LiFP6.Finally, it should be noted that the respective above embodiments are only for illustrating and not limiting the technical solutions of the present application; however, although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the above embodiments or make equivalent substitutions on some or all of the technical features; however, these modifications or substitutions do not lead to the spirit of the respective technical solutions deviating from the scope of the technical solutions of the embodiments of the present application.

Claims

A winding core (100), characterized in that the winding core (100) comprises a first electrode plate (10), a separator (20), and a second electrode plate (30) stacked and wound one after another, the polarities of the first electrode plate (10) and the second electrode plate (30) being opposite to each other; wherein the first electrode plate (10) is provided with a first tab (40), the second electrode plate (30) is provided with a step groove (33) disposed opposite to the first tab (40), the step groove (33) comprises a first groove (331) and a second groove (332) disposed opposite to the first tab (40) and connected one after another, the projection of the second groove (332) along the thickness direction of the winding core (100) being disposed within the projection of the first groove (331); wherein a side of a winding rear end of the first electrode plate (10) facing the second electrode plate (30) has an active layer rear portion and a finish tape (60), the head of the finish tape (60) covering the active layer rear portion; wherein the orthogonal projection in the thickness direction of the winding core (100), the head of the finish tape (60), and the active layer rear portion are all disposed in the second groove (332).The winding core (100) according to claim 1, characterized in that the first electrode plate (10) includes a first current collector (11), and first and second active layers (13; 14) each disposed on two opposite sides of the first current collector (11) in the thickness direction, wherein along the winding direction in the active layer rear portion, a rear end of the first active layer is flush with a rear end of the second active layer; or wherein the rear end of the first active layer exceeds the rear end of the second active layer; or wherein the rear end of the second active layer exceeds the rear end of the first active layer.The winding core (100) according to claim 1 or 2, characterized in that the step groove (33) comprises a third groove (333) arranged facing away from the first groove (331) and connected to the second groove (332), wherein the projection of the third groove (333) along the thickness direction of the winding core (100) is arranged within the projection of the second groove (332), wherein the first step surface (334) of the first groove (331) and the third step surface (336) of the third groove (333) are respectively on both sides of the second step surface (335) of the second groove (332); wherein the depth of the first step surface (334) is h1, wherein the depth of the second step surface (335) is h2, wherein the depth of the third step surface (336) is h3, and wherein h1, h2 and h3 satisfy the condition 0<h1≤h2≤h3.The winding core (100) according to claim 3, characterized in that the first electrode plate (10) comprises a first current collector (11) and first active material layers (12) respectively disposed on two opposite sides of the first current collector (11) in the thickness direction, the second electrode plate (30) comprises a second current collector (31) and second active material layers (32) respectively disposed on two opposite sides of the second current collector (31) in the thickness direction; wherein h1 satisfies the condition h1 < h3 - thickness of the first tab (40); and / or wherein h2 satisfies the condition h2 < h3 - 2 * thickness of the first active material layer (12); and / or wherein h3 satisfies the condition h3 is equal to the thickness of the second active material layer (32).Winding core (100) according to Claim 4, characterized in that h1 satisfies the condition h1 = h3 - 1 / 2 * thickness of the first tab (40); and / or wherein h2 satisfies the condition h2 = h3 - thickness of the first active material layer (12).Winding core (100) according to one of Claims 1 to 5, characterized in that an end groove is provided at the winding rear end of the first electrode plate (10), in which end groove the head of the adhesive end strip (60) is arranged.The winding core (100) according to any one of claims 1 to 6, characterized in that the winding core (100) further comprises a first protective adhesive tape (70), wherein the first protective adhesive tape (70) is disposed on the first electrode plate (10), and wherein the first protective adhesive tape (70) covers the first tab (40), wherein the first protective adhesive tape (70) extends along the winding direction of the winding core (100) and at least partially covers the sheet segment (200) of the winding core (100) on a side closest to the first tab (40).The winding core (100) according to any one of claims 1 to 7, characterized in that the winding core (100) further comprises a second protective adhesive tape, wherein the second protective adhesive tape is disposed on the second electrode plate (30), and wherein the second protective adhesive tape covers the step groove (33).The winding core (100) according to any one of claims 1 to 8, characterized in that a gap is formed between the edge of the step groove (33) and the edge of the second electrode plate (30) in the width direction of the second electrode plate (30).The winding core (100) according to any one of claims 1 to 9, characterized in that the first electrode plate (10) includes a first current collector (11) and first active material layers (12) respectively disposed on two opposite sides of the first current collector (11) in the thickness direction, a first recess (123) being formed on the first active material layer (12); and / or wherein the second electrode plate (30) includes a second current collector (31) and second active material layers (32) respectively disposed on two opposite sides of the second current collector (31) in the thickness direction, a second recess (34) being formed on the second active material layer (32).A battery, characterized in that the battery comprises a housing and a winding core (100) according to any one of claims 1 to 10, wherein the winding core (100) is arranged in the housing.

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