Positive pole piece, battery cell and lithium ion battery
By embedding an insulating layer within the active material layer of the positive electrode sheet of a lithium-ion battery, the insulating layer isolates the current collector from the active material layer during thermal expansion, thus solving the thermal runaway problem caused by short circuits in lithium-ion batteries, improving safety performance and maintaining cycle performance.
Patent Information
- Application Number
- CN202421680939.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-16
- Publication Date
- 2025-11-11
- Estimated Expiration
- 2034-07-16
AI Technical Summary
When lithium-ion batteries are subjected to mechanical damage, the positive electrode active layer is prone to short circuit with the negative electrode current collector, which can cause thermal runaway and affect cycle performance.
An insulating layer is embedded within the active material layer of the positive electrode. When heated, the insulating layer expands to isolate the current collector from the active material layer, increasing internal resistance to prevent thermal runaway caused by short circuits, while not affecting conductivity during normal use.
It effectively avoids thermal runaway caused by short circuits in lithium-ion batteries, improves safety performance, and maintains good cycle performance.
Smart Images
Figure CN223539604U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of lithium-ion battery technology, and in particular to a positive electrode sheet, a battery cell, and a lithium-ion battery. Background Technology
[0002] Lithium-ion batteries are batteries that contain lithium (including metallic lithium, lithium alloys, lithium ions, and lithium polymers) in their electrochemical system. In recent years, lithium-ion batteries have been widely used in digital products, electric vehicles, and energy storage systems due to their many advantages, such as long cycle life, good safety performance, and fast charging and discharging.
[0003] Currently, when lithium-ion batteries are subjected to mechanical damage (such as impact or compression), it can lead to a short circuit between the positive electrode active layer and the negative electrode current collector, or even direct contact between the negative electrode active layer and the positive electrode active layer, causing thermal runaway. To avoid this thermal runaway problem, the traditional approach is to apply a protective layer with low conductivity to the surface of the positive electrode current collector to prevent short circuits. However, since this protective layer is directly coated on the surface of the positive electrode current collector, it will affect the conductivity of the positive electrode active layer when in contact with it, thus impacting the battery's cycle performance. Utility Model Content
[0004] The main purpose of this invention is to propose a positive electrode sheet, a battery cell, and a lithium-ion battery, aiming to solve the technical problems of existing lithium-ion batteries being prone to thermal runaway and deterioration of cycle performance under mechanical damage.
[0005] To achieve the above objectives, this utility model proposes a positive electrode sheet for use in lithium-ion batteries, wherein the positive electrode sheet comprises:
[0006] current collector;
[0007] An active material layer is disposed on the surface of the current collector;
[0008] An insulating layer is embedded in the active material layer, and the insulating layer is used to expand when heated to isolate the current collector from the active material layer.
[0009] In some embodiments, the insulating layer has an initial state and an expanded state;
[0010] In the initial state, the insulating layer is embedded within the active material layer;
[0011] In the expanded state, the insulating layer extends at least partially between the active material layer and the current collector, thereby separating the current collector from the active material layer.
[0012] In some embodiments, the active material layer has a first surface facing the current collector and a second surface facing away from the current collector;
[0013] In the initial state, the distance from the insulating layer to the first surface is less than the distance to the second surface.
[0014] In some embodiments, the thickness of the insulating layer in the initial state is less than the thickness of the active material layer, and the thickness of the insulating layer in the expanded state is greater than the thickness of the active material layer; and / or,
[0015] The thickness of the insulating layer in the expanded state is 1.2-1.5 times the thickness of the active material layer.
[0016] In some embodiments, the thickness of the active material layer is 25 μm-30 μm; and / or,
[0017] The thickness of the insulating layer in the initial state is 15μm-20μm.
[0018] In some embodiments, the insulating layer includes at least two thermal expansion bodies, which are embedded at intervals within the active material layer.
[0019] In some embodiments, the at least two thermal expansion bodies are equally spaced and embedded in the active material layer along the length direction of the active material layer, and the total projection of the insulating layer in the thickness direction of the current collector accounts for 30%-60% of the projection of the active material layer in the thickness direction of the current collector.
[0020] In some embodiments, the distance between two adjacent thermal expansion bodies is 100μm-500μm.
[0021] This utility model also provides a battery cell, including a negative electrode, a separator, and a positive electrode as described above, wherein the separator is disposed between the positive electrode and the negative electrode.
[0022] This utility model also provides a lithium-ion battery, including a casing and a battery cell as described above, wherein the battery cell is disposed inside the casing.
[0023] The positive electrode sheet for lithium-ion batteries provided by this invention features an insulating layer embedded within the active material layer. This insulating layer expands upon heating to isolate the current collector from the active material layer. When an internal short circuit occurs due to an external impact, causing a rapid increase in internal temperature, the insulating layer expands upon heating to isolate the current collector from the active material layer, increasing the internal resistance of the lithium-ion battery and thus preventing thermal runaway caused by the short circuit. Simultaneously, because the insulating layer is embedded within the active material layer, it does not affect the contact conductivity between the active material layer and the current collector during normal use of the lithium-ion battery. This allows the lithium-ion battery of this invention to balance safety and cycle performance. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the structure of an embodiment of the positive electrode sheet of this utility model;
[0025] Figure 2 This is a schematic diagram of the expanded structure of an embodiment of the positive electrode sheet of this utility model.
[0026] Explanation of icon numbers:
[0027]
[0028]
[0029] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0030] The solutions in the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. Based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this utility model.
[0031] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in this utility model embodiment are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.
[0032] It should also be noted that when a component is described as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intervening component present. When a component is described as "connected to" another component, it can be directly connected to the other component or there may be an intervening component present.
[0033] Furthermore, the use of terms such as "first" and "second" in this utility model is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this utility model.
[0034] Please refer to Figure 1 and Figure 2 This utility model proposes a positive electrode 100 for use in lithium-ion batteries. The positive electrode 100 provided in this embodiment includes:
[0035] Current collector 10. The current collector 10 can be aluminum foil or aluminum foil, used to collect current.
[0036] An active material layer 20 is disposed on the surface of the current collector 10. The active material layer 20 is composed of oxidants with relatively positive potential and stable in the electrolyte, such as metal oxides such as manganese dioxide, lead dioxide, and nickel oxide, oxygen or air, halogens and their salts, oxyacids and their salts, etc.
[0037] An insulating layer 30 is embedded in the active material layer 20. The insulating layer 30 is used to expand when heated to isolate the current collector 10 from the active material layer 20.
[0038] When the internal temperature of a lithium-ion battery rises sharply due to an internal short circuit caused by an external impact, the insulating layer 30 can absorb the heat released by the short circuit and expand to isolate the current collector 10 from the active material layer 20, thereby increasing the internal resistance of the lithium-ion battery and preventing thermal runaway caused by the temperature rise due to the short circuit. At the same time, since the insulating layer 30 is embedded in the active material layer 20, it will not affect the contact conductivity between the active material layer 20 and the current collector 10 during normal use of the lithium-ion battery, so that the lithium-ion battery of this invention takes into account both safety performance and cycle performance.
[0039] In some embodiments, the insulating layer 30 has an initial state and an expanded state;
[0040] In the initial state, the insulating layer 30 is embedded in the active material layer 20, and will not affect the contact conductivity between the active material layer 20 and the current collector 10 when the lithium-ion battery is in normal use.
[0041] In the expanded state, the insulating layer 30 extends at least partially between the active material layer 20 and the current collector 10, thereby separating the current collector 10 from the active material layer 20. Specifically, when the insulating layer 30 is heated, at least part of the insulating layer 30 extends beyond the active material layer 20 and connects with the current collector 10, pushing the current collector 10 and the active material layer 20 apart to increase the internal resistance of the lithium-ion battery, thereby preventing thermal runaway caused by temperature rise due to short circuit.
[0042] In some embodiments, the active material layer 20 has a first surface 31 facing the current collector 10 and a second surface 32 facing away from the current collector 10; in the initial state, the distance from the insulating layer 30 to the first surface 31 is less than the distance to the second surface 32. Thus, when the insulating layer 30 expands due to heat, the first surface 31 can extend between the active material layer 20 and the current collector 10, thereby separating the current collector 10 from the active material layer 20, while the second surface 32 remains within the active material layer 20.
[0043] In some embodiments, the thickness of the insulating layer 30 in the initial state is less than the thickness of the active material layer 20, so that the insulating layer 30 can be embedded in the active material layer 20 without affecting the normal contact and conductivity between the active material layer 20 and the current collector 10; the thickness of the insulating layer 30 in the expanded state is greater than the thickness of the active material layer 20, so that the insulating layer 30 can isolate the active material layer 20 and the current collector 10.
[0044] In some embodiments, the thickness of the insulating layer 30 in the expanded state is 1.2 to 1.5 times the thickness of the active material layer 20.
[0045] In some embodiments, the thickness of the active material layer 20 is 25 μm-30 μm; the thickness of the insulating layer 30 in the initial state is 15 μm-20 μm.
[0046] In some embodiments, the insulating layer 30 includes at least two thermal expansion bodies 33, which are embedded in the active material layer 20 at intervals. The total projection of the insulating layer 30 in the thickness direction of the current collector 10 accounts for 30%-60% of the projection of the active material layer 20 in the thickness direction of the current collector 10.
[0047] In this embodiment, the thermally expanding body 33 is made of a thermally expanding material. When the internal temperature rises due to a short circuit in the lithium-ion battery, it absorbs the heat released by the short circuit and expands towards the current collector 10 to separate the current collector 10 from the active material layer 20. The thermally expanding material refers to a material whose volume expands with increasing temperature, such as expandable microspheres (thermoplastic hollow polymer microspheres), etc. This embodiment includes, but is not limited to, these.
[0048] In this embodiment, the active material is coated onto the surface of the current collector 10 to form an active material layer 20. Then, at least two thermally expanded bodies 33 are embedded in the active material layer 20 by rolling, and the adhesiveness of the active material layer 20 ensures that the thermally expanded bodies 33 at different positions have a certain spacing. The positive electrode sheet 100 of this embodiment has a simple processing technology, which can effectively reduce production costs compared with the traditional positive electrode material protective layer set on the surface of the current collector. Moreover, the rolling process further improves the flatness of the surface of the positive electrode sheet 100 and improves the safety performance of the lithium-ion battery.
[0049] In some embodiments, at least two thermal expansion bodies 33 are equally spaced and embedded in the active material layer 20 along the length direction of the active material layer 20, that is, at least two thermal expansion bodies 33 are uniformly distributed in the active material layer 20. In this way, when the thermal expansion bodies 33 are heated and expand and extend to the active material layer 20 to connect with the current collector 10, they can act uniformly on the current collector 10, so that the current collector 10 can move stably.
[0050] In some embodiments, the distance between two adjacent thermal expansion bodies 33 is 100μm-500μm. The distance between two adjacent thermal expansion bodies 33 can be selected within the range of 100μm-500μm depending on the actual situation. A suitable distance between two adjacent thermal expansion bodies 33 serves two purposes: firstly, it isolates the active material layer 20 from the current collector 10, preventing thermal runaway in the lithium-ion battery; secondly, it avoids the situation where the distance is too large, making it impossible to isolate the active material layer 20 from the current collector 10, or too small, increasing the processing difficulty and production cost of the positive electrode 100.
[0051] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and do not limit the scope of the present invention.
[0052] Example 1
[0053] This embodiment provides a positive electrode 100, and the preparation method of the positive electrode 100 is as follows:
[0054] S1: NCM7205, conductive agent (conductive carbon black), and PVDF are mixed in a ratio of 95:2:3 to prepare an active material. The active material is uniformly coated on a 12μm copper foil surface with a thickness of 28μm.
[0055] S2: The insulating layer 30 (22μm) is embedded into the active material layer 20 by roll pressing, and the thickness of the positive electrode 100 after roll pressing is 26μm.
[0056] Example 2
[0057] This embodiment provides a positive electrode 100, and the preparation method of the positive electrode 100 is as follows:
[0058] S1: NCM811, conductive agent (conductive carbon black), and PVDF are mixed in a ratio of 96:3:2 to prepare an active material. The active material is uniformly coated on a 12μm copper foil surface with a thickness of 30μm.
[0059] S2: The insulating layer 30 (26μm) is embedded into the active material layer 20 by roll pressing, and the thickness of the positive electrode 100 after roll pressing is 28μm.
[0060] Comparative Example 1:
[0061] This comparative example provides a positive electrode sheet, using NCM7205 as the positive electrode material, with all other parameters being the same, and prepared using conventional processes.
[0062] Comparative Example 2:
[0063] This comparative example provides a positive electrode sheet, using NCM811 as the positive electrode material, with all other parameters being the same, and prepared using conventional processes.
[0064] The positive electrode sheets 100 prepared by the processes of Examples 1-2 and Comparative Examples 1-2 were assembled into 5Ah soft-pack cells, and temperature distribution simulation tests, external short circuit tests, and needle penetration tests were performed. The test results are shown in Table 1.
[0065] serial number Cell surface temperature (°C) External short circuit Battery status after needle puncture Example 1 28-35 No change in appearance No fire or explosion Example 2 30-31 No change in appearance No fire or explosion Comparative Example 1 50-66 Battery bulging Fire and explosion Comparative Example 2 49-60 Battery bulging Fire and explosion
[0066] Table 1
[0067] As can be seen from Table 1 above, the positive electrode 100, the battery cell, and the lithium-ion battery prepared by this invention have good safety and can avoid thermal runaway caused by temperature rise due to short circuit.
[0068] This utility model also provides a battery cell, including a negative electrode, a separator, and a positive electrode 100 as described above, with the separator disposed between the positive and negative electrode. Since this battery cell adopts all the technical solutions of all the above embodiments, it possesses at least all the technical effects brought about by the technical solutions of the above embodiments, which will not be elaborated upon here.
[0069] This utility model also provides a lithium-ion battery, including a casing and a battery cell as described above, with the battery cell disposed within the casing. Since this lithium-ion battery employs all the technical solutions of all the above embodiments, it possesses at least all the technical effects brought about by the technical solutions of the above embodiments, and will not be elaborated upon further here.
[0070] The above embodiments of this utility model are merely examples for clearly illustrating the present utility model, and are not intended to limit the implementation of the present utility model. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this utility model are still within the protection scope of this utility model.
Claims
1. A positive electrode sheet, used in lithium-ion batteries, characterized in that, The positive electrode sheet includes: current collector; An active material layer is disposed on the surface of the current collector; An insulating layer is embedded in the active material layer, and the insulating layer is used to expand when heated to isolate the current collector from the active material layer; The insulating layer includes at least two thermal expansion bodies, which are embedded in the active material layer at intervals. The total projection of the insulating layer in the thickness direction of the current collector accounts for 30%-60% of the projection of the active material layer in the thickness direction of the current collector.
2. The positive electrode sheet according to claim 1, characterized in that, The insulating layer has an initial state and an expanded state; In the initial state, the insulating layer is embedded within the active material layer; In the expanded state, the insulating layer extends at least partially between the active material layer and the current collector, thereby separating the current collector from the active material layer.
3. The positive electrode sheet according to claim 2, characterized in that, The active material layer has a first surface facing the current collector and a second surface facing away from the current collector; In the initial state, the distance from the insulating layer to the first surface is less than the distance to the second surface.
4. The positive electrode sheet according to claim 2 or 3, characterized in that, The thickness of the insulating layer in the initial state is less than the thickness of the active material layer, and the thickness of the insulating layer in the expanded state is greater than the thickness of the active material layer; and / or, The thickness of the insulating layer in the expanded state is 1.2-1.5 times the thickness of the active material layer.
5. The positive electrode sheet according to claim 2 or 3, characterized in that, The thickness of the active material layer is 25μm-30μm; and / or, The thickness of the insulating layer in the initial state is 15μm-20μm.
6. The positive electrode sheet according to claim 1, characterized in that, The at least two thermally expandable bodies are embedded in the active material layer at equal intervals along the length of the active material layer.
7. The positive electrode sheet according to claim 1, characterized in that, The distance between two adjacent thermal expansion bodies is 100μm-500μm.
8. A battery cell, characterized in that, It includes a negative electrode, a separator, and a positive electrode as described in any one of claims 1 to 7, wherein the separator is disposed between the positive electrode and the negative electrode.
9. A lithium-ion battery, characterized in that, It includes a housing and a battery cell as described in claim 8, wherein the battery cell is disposed within the housing.