Pole piece, roll core and battery
By providing a buffer portion in the asymmetric region of the active layer of the lithium-ion battery electrode sheet, the problem of uneven pressure at the junction of the electrode sheet is solved, the embeddedness of lithium ions is improved, and the service life of the battery is extended.
Patent Information
- Application Number
- CN202420159990.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-22
- Publication Date
- 2024-12-17
- Estimated Expiration
- 2034-01-22
AI Technical Summary
At the junction of single and double layers of the electrode sheet of lithium-ion batteries, it is difficult to immerse lithium due to uneven pressure, affecting the circulation service life.
Design an extreme sheet in which the active layer is provided with a buffer portion in an asymmetric region, the height of the buffer portion is gradually reduced from the surface of the active layer to the current collector surface to disperse the pressure at the junction and passes through a stepped, curved or triangular prism. The buffer structure improves the uniformity of pressure.
It effectively avoids overvoltage at the junction of the pole sheet, ensures that lithium ions can be easily embedded in the active layer, and improves the battery's recycling life.
Smart Images
Figure CN222190865U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the field of lithium batteries, and in particular to a pole piece, a winding core and a battery. Background Art
[0002] Lithium-ion secondary batteries have become one of the most widely used secondary batteries due to their advantages of high voltage and high energy density. With the continuous development of miniaturization and long standby of portable electronic devices, the energy density, especially the volume energy density, of lithium-ion batteries as power sources has been continuously improved to meet the increasing demand.
[0003] Conventional wound lithium-ion batteries are made up of anode sheets, separators, and cathode sheets stacked and wound in sequence. In order to improve space utilization, the head area of the anode sheet and cathode sheet is composed of a partial single-layer active material layer and a partial double-layer active material layer, such as Figure 1 This also causes the interface between the single-layer active material layer and the double-layer active material layer to be subjected to greater pressure during rolling. This will make it difficult to embed lithium at the interface during the cyclic charge and discharge process after the battery is made, which will lead to lithium precipitation and affect the cycle life. Utility Model Content
[0004] The main purpose of the utility model is to provide a pole piece, aiming to solve the problem of unbalanced pressure at the junction of the single and double layers of the pole piece.
[0005] In order to achieve the above-mentioned purpose, the utility model provides a pole piece, which comprises:
[0006] A current collector has a first surface and a second surface relative to each other, wherein at least portions of the first surface and the second surface are covered with an active layer, wherein a buffer portion is constructed on one side of one active layer, and the height of the buffer portion gradually decreases from the surface of the active layer to the surface of the current collector, and with the surface of the current collector as a projection plane, the projection of the free end of the buffer portion is located within the projection range of another active layer.
[0007] In some embodiments, the width L of the buffer portion ranges from 1 mm to 4 mm.
[0008] In some embodiments, the buffer portion is arranged in a stepped shape.
[0009] In some embodiments, the buffer portion is configured with a plurality of steps, and widths of the plurality of steps are equal.
[0010] In some embodiments, the buffer portion is structured with three steps. Assuming that the heights of the steps are H1, H2, and H3, respectively, and the thickness of the active layer is H, the relationship satisfies:
[0011] H1+H2+H3=H, 1 / 4H≤H1≤1 / 2H, 1 / 4H≤H2≤1 / 2H, 1 / 4H≤H3≤1 / 2H.
[0012] In some embodiments, the buffer portion is configured as a curved surface.
[0013] In some embodiments, the buffer portion is configured as an inclined surface.
[0014] In some embodiments, the active layers each include an adhesive, a conductive agent, and an active material.
[0015] The utility model further proposes a winding core, which includes a diaphragm and two pole pieces with opposite polarities located on both sides of the diaphragm; at least one of the two pole pieces is the pole piece described in any one of the aforementioned embodiments.
[0016] The utility model further provides a battery, which comprises a shell and the winding core in the above-mentioned embodiment, wherein the winding core is arranged in the shell.
[0017] The utility model provides a buffer portion in the asymmetric area of the active layer, thereby preventing the junction of the two active layers from being subjected to excessive pressure during rolling, ensuring that there are sufficient pores in the active layer so that lithium ions can be easily embedded in the active layer, thereby improving the cycle life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 It is a structural schematic diagram of an embodiment of a pole piece in the prior art;
[0019] Figure 2 It is a structural schematic diagram of another embodiment of a pole piece in the prior art;
[0020] Figure 3 It is a structural schematic diagram of another embodiment of a pole piece in the prior art;
[0021] Figure 4 This is a schematic structural diagram of an embodiment of a pole piece of the utility model;
[0022] Figure 5 It is a structural schematic diagram of another embodiment of the pole piece of the utility model;
[0023] Figure 6 It is a structural schematic diagram of another embodiment of the pole piece of the utility model. DETAILED DESCRIPTION
[0024] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the scheme in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.
[0025] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back...) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.
[0026] It should also be noted that when an element is referred to as being "fixed on" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element at the same time. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.
[0027] In addition, the descriptions of "first", "second", etc. in the present utility model are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present utility model.
[0028] The utility model proposes a pole piece, referring to Figure 4-Figure 6 , the pole piece comprises:
[0029] The current collector 10 has a first surface and a second surface relative to each other, and at least part of the first surface and the second surface is covered with an active layer 20, wherein a buffer portion is constructed on one side of one active layer 20, and the height of the buffer portion gradually decreases from the surface of the active layer 20 to the surface of the current collector 10. Taking the surface of the current collector 10 as the projection surface, the projection of the free end of the buffer portion is located within the projection range of the other active layer 20.
[0030] Common materials for the current collector 10 include metal foils, such as copper foil and aluminum foil, and composite materials. The positive and negative electrodes of the battery can be formed by coating the electrode materials on the current collector 10. In this embodiment, active layers 20 are provided on both surfaces of the current collector 10 to improve the utilization rate of the current collector 10 and form pole pieces.
[0031] Since the expansion of the pole piece is taken into consideration in the battery design, a certain space needs to be designed to accommodate the increase in thickness caused by the expansion of the pole piece, that is, the group margin design. The group margin refers to the ratio of the actual internal cross-sectional area of the battery cell to the maximum internal cross-sectional area. Taking the wound battery cell as an example, the battery cell is cut horizontally, and the ratio of the cross-sectional area of each material of the wound electrode assembly to the area contained in the inner diameter of the battery cell shell is obtained. Therefore, by setting the active layer 20 on both sides of the current collector 10 to an asymmetrical form, that is, taking the surface of the current collector 10 as the projection surface, the projections of the two active layers 20 do not completely overlap, the volume of the battery cell after winding can be made smaller, and the internal space of the battery can be saved under the condition that the group margin remains unchanged, and the number of layers of the bare battery cell can be increased by using the saved space to increase the capacity; or under the premise that the battery design capacity remains unchanged, the thickness of the bare battery cell is reduced, and the group margin of the entire battery cell is reduced, so that the volume of the battery is smaller. The specific way of setting the active layer 20 includes several different situations, which are explained by the following embodiments.
[0032] Embodiment 1: Figure 1 As shown, the active layers 20 respectively disposed on the two surfaces of the current collector 10 are symmetrical only at one end and asymmetrical at the other end.
[0033] Embodiment 2: Figure 2 and Figure 3 As shown, both ends of the active layer 20 respectively disposed on the two surfaces of the current collector 10 are asymmetric.
[0034] However, during the production of the pole piece, the current collector 10 and the active layer 20 coated on the current collector 10 need to be rolled, and the asymmetric active layer 20 will cause excessive pressure on the junction of the two active layers 20 during rolling, making the pores in the active layer 20 that accommodate lithium ions smaller, thereby affecting the insertion of lithium ions and causing lithium precipitation. Therefore, according to the situation, a buffer is constructed on one side of at least one active layer 20, and the height of the buffer is gradually reduced from the surface of the active layer 20 to the surface of the current collector 10, so that the pressure on the junction is dispersed to the buffer, thereby avoiding overpressure at the junction of the two active layers 20.
[0035] It can be understood that the material used for the buffer is usually the same as that of the active layer 20. If the materials of the active layer 20 coated on the upper and lower surfaces of the current collector 10 are different, the material of the buffer is the same as that of the active layer 20 directly connected to the buffer. For example, the active layers 20 on both sides of the current collector 10 are divided into the first active layer 20 and the second active layer 20. If the buffer is connected to the first active layer 20, the material of the buffer is the same as that of the first active layer 20; if the buffer is connected to the second active layer 20, the material of the buffer is the same as that of the second active layer 20.
[0036] like Figure 4-Figure 6As shown, in a preferred embodiment, the length L of the buffer portion 40 ranges from 1 mm to 4 mm.
[0037] Among them, since the size of the active layer 20 is related to the battery model, the length of the asymmetric area of the active layer 20 on the first surface and the second surface of the current collector 10 is usually 100mm~160mm. In order to ensure that the buffer part 40 plays a corresponding role, the length range of the buffer part 40 is limited to between 1mm and 4mm, which can be 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm.
[0038] When the length of the buffer portion 40 is 1mm, the improvement effect at the junction of the upper and lower active layers 20 is small, and if the length of the buffer portion 40 is further reduced, the improvement effect of the buffer portion 40 will be greatly reduced; when the length of the buffer portion 40 is 4mm, the improvement effect at the junction of the upper and lower active layers 20 is large, and if the length of the buffer portion 40 is further increased, its effect will be further increased, but it will also increase the thickness of the electrode after rolling up, which is easy to affect the charge and discharge performance and thickness of the battery, thereby reducing the application scenario of the battery. Preferably, the length of the buffer portion 40 is selected to be 2.5mm, which has a sufficient improvement effect on the junction of the upper and lower active layers 20 while ensuring that the thickness of the electrode is less affected.
[0039] like Figure 4 As shown, in a preferred embodiment, the buffer portion is arranged in a stepped shape.
[0040] The buffer portion 40 is set to be stepped, and the height gradually decreases from the surface of the active layer 20 to the surface of the current collector 10, so that when the pole piece is rolled, the junction of the upper and lower active layers 20 is protected by the stepped buffer portion 40, and the pressure is more uniform, thereby avoiding the difficulty of lithium insertion. In addition, the stepped buffer portion 40 can also increase the uniformity of the active layer 20 after pressure, reduce the protrusions that may appear at the end of the active layer 20, and improve the flatness of the active layer 20. It can be understood that the highest point of the buffer portion 40 is controlled not to be higher than the active layer 20 to avoid affecting the performance of the pole piece.
[0041] like Figure 4 As shown, in a preferred embodiment, the buffer portion 40 has a plurality of steps, and the widths of the plurality of steps are equal.
[0042] The more steps there are, the better the effect after rolling, but the coating difficulty will increase accordingly. The number of steps can be controlled as needed. At the same time, the width of each step is made equal to improve the uniformity of the buffer part 40, so that the surface of the pole piece after rolling is smoother.
[0043] like Figure 4As shown, in some embodiments, the stepped shape has three steps, the heights of the steps are H1, H2, and H3 respectively, the thickness of the active layer 20 is H, and the relationship satisfies:
[0044] H1+H2+H3=H, 1 / 4H≤H1≤1 / 2H, 1 / 4H≤H2≤1 / 2H, 1 / 4H≤H3≤1 / 2H.
[0045] The three-step ladder can effectively improve the overvoltage situation at the junction, while not increasing the coating difficulty of the transition section too much. The height of the step is controlled within a certain range to further improve the uniformity of the buffer portion 40 and avoid the emergence of a new overvoltage area due to a large drop between the steps. Preferably, the heights H1, H2 and H3 of the three-step ladder are controlled to be equal, that is, the heights of the three steps are equal, which reduces the processing difficulty and improves the flatness of the pole piece.
[0046] like Figure 5 As shown, in some embodiments, one surface of the buffer portion 40 is a curved surface.
[0047] One side of the curved surface is an arc, and the convex direction of the arc can be inward or outward, which is not limited in this application. Preferably, the height drop speed of the buffer portion 40 is fast at first and then slow, that is, the convexity of the arc is outward, in a parabolic shape, so that the end close to the active layer 20 is higher as a whole, which is convenient for bearing rolling pressure and improving the pressure condition at the junction of the two active layers 20.
[0048] like Figure 6 As shown, in some embodiments, the buffer portion 40 is configured in a triangular prism shape.
[0049] Similar to the above-mentioned embodiment, no further description is given here. It is worth mentioning that the triangular prism-shaped transition section is less difficult to coat and is more convenient for large-scale production.
[0050] In some embodiments, the active layer 20 includes a binder, a conductive agent, and an active material.
[0051] Among them, the active material may include at least one of lithium iron phosphate, lithium cobaltate, lithium manganate, ternary system, lithium titanate and other lithium transition metal oxides, usually accounting for 60-99.8% of the total mass in the composition; the conductive agent may include at least one of various activated carbons, carbon nanotubes, graphene, hollow graphene balls, carbon black, acetylene black, carbon fiber, Ketjen black, etc., usually accounting for 0.5-40% of the total mass in the composition; the binder may include at least one of polyvinylidene fluoride, styrene butadiene rubber, methyl cellulose phosphate, polytetrafluoroethylene, polyolefin, usually accounting for 0.5-40% of the total mass in the composition; the auxiliary additive may include at least one of dispersant, flame retardant, ceramic powder, metal powder, leveling agent, defoamer, lithium supplement, filler, etc., usually accounting for 0-20% of the total mass in the composition. It can be understood that the materials of the active layer 20 on both surfaces of the current collector can be the same or different, and different types of pole pieces can be made by using different active layer 20 materials, and this application does not limit this.
[0052] The utility model further proposes a winding core, which includes a diaphragm and two pole pieces located on both sides of the diaphragm and having opposite polarities; at least one of the two pole pieces is the pole piece of any one of the aforementioned embodiments.
[0053] Since the present winding core adopts all the technical solutions of all the above-mentioned embodiments, it has at least all the technical effects brought by the technical solutions of the above-mentioned embodiments, which will not be described one by one here.
[0054] The utility model further provides a battery, which comprises a shell and the winding core in the above-mentioned embodiment, wherein the winding core is arranged in the shell.
[0055] The specific structure of the winding core refers to the above-mentioned embodiments. Since the battery adopts all the technical solutions of all the above-mentioned embodiments, it has at least all the technical effects brought by the technical solutions of the above-mentioned embodiments, which will not be described one by one here.
[0056] The above description is only a partial or preferred embodiment of the present invention. Neither the text nor the drawings can limit the scope of protection of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the overall concept of the present invention, or direct / indirect application in other related technical fields are included in the scope of protection of the present invention.
Claims
1. A pole piece, characterized in that: The pole piece includes: A current collector having a first surface and a second surface relative to each other, wherein at least portions of the first surface and the second surface are covered with an active layer, and a buffer portion is configured on one side of at least one active layer, wherein the height of the buffer portion gradually decreases from the surface of the active layer to the surface of the current collector, and the projection of the free end of the buffer portion is located within the projection range of another active layer, with the surface of the current collector being used as a projection plane.
2. The pole piece according to claim 1, characterized in that: The width L of the buffer portion is in the range of 1 mm to 4 mm.
3. The pole piece according to claim 2, characterized in that: The buffer portion is arranged in a stepped shape.
4. The pole piece according to claim 3, characterized in that: The buffer portion is configured with a plurality of steps, and the widths of the plurality of steps are equal.
5. The pole piece according to claim 4, characterized in that: The buffer portion is structured with three steps. Assuming that the heights of the steps are H1, H2, and H3 respectively, and the thickness of the active layer is H, the relationship satisfies: H1+H2+H3=H, 1 / 4H≤H1≤1 / 2H, 1 / 4H≤H2≤1 / 2H, 1 / 4H≤H3≤1 / 2H.
6. The pole piece according to claim 2, characterized in that: One surface of the buffer portion is a curved surface.
7. The pole piece according to claim 2, characterized in that: The buffer portion is arranged in a triangular prism shape.
8. The pole piece according to any one of claims 1 to 7, characterized in that: The active layer includes an adhesive, a conductive agent and an active material.
9. A winding core, characterized in that: The winding core includes a diaphragm and two pole pieces with opposite polarities located on both sides of the diaphragm; at least one of the two pole pieces is the pole piece described in any one of claims 1-8.
10. A battery, characterized in that: The battery comprises a casing and the winding core as claimed in claim 9, wherein the winding core is disposed in the casing.