An electric cell

Abstract

The application discloses a kind of battery. The battery of the application includes positive pole piece group, diaphragm and negative pole piece arranged in sequence along the thickness direction of battery, positive pole piece group includes first positive pole piece and second positive pole piece arranged at intervals along winding direction, along the thickness direction of battery, part second positive pole piece is located in the outside of first positive pole piece, first positive pole piece is coated with first coating layer including first active material, second positive pole piece is coated with second coating layer including second active material, the mass percentage of first active material in first coating layer is greater than the mass percentage of second active material in second coating layer. First positive pole piece and negative pole piece, and second positive pole piece and negative pole piece form independent charge-discharge system, and can output voltage simultaneously to realize high rate discharge when discharging, at the same time, the setting of first coating layer and second coating layer can increase the short-circuit resistance between the negative pole piece when internal short circuit occurs, avoid fire, and improve the safety of battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a battery cell. Background Technology

[0002] Among related technologies, lithium-ion batteries have been increasingly widely used due to their advantages such as long cycle life, superior rate performance, and high energy density. Lithium-ion batteries with characteristics such as large capacity, high safety, and high-rate charge and discharge are the future development direction of lithium-ion batteries. However, in the current technology, the cells are prone to short circuits and overheating when discharged at high rates, and are also very easy to catch fire when subjected to external impacts, so the safety of the cells cannot be guaranteed. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a battery cell that can achieve high-rate discharge while maintaining good safety.

[0004] According to a first aspect of the present invention, a battery cell includes a positive electrode group, a separator, and a negative electrode arranged sequentially along the thickness direction of the battery cell. The positive electrode group includes a first positive electrode and a second positive electrode arranged at intervals along the winding direction. Along the thickness direction of the battery cell, at least a portion of the second positive electrode is located outside the first positive electrode. At least one tab is provided on the first positive electrode, the second positive electrode, and the negative electrode.

[0005] The first positive electrode includes a first current collector, and a first coating is applied to both sides of the first current collector. The second positive electrode includes a second current collector, and a second coating is applied to both sides of the second current collector. The first coating includes a first active material, and the second coating includes a second active material. The mass percentage of the first active material in the first coating is greater than the mass percentage of the second active material in the second coating.

[0006] The battery cell according to embodiments of the present invention has at least the following beneficial effects: independent charging and discharging systems are formed between the first positive electrode and the negative electrode, and between the second positive electrode and the negative electrode. During discharge, the two systems can output simultaneously to achieve high-rate discharge. At the same time, the second positive electrode at least partially covers the outside of the first positive electrode. A first coating is applied to both sides of the first current collector, and a second coating is applied to both sides of the second current collector. The mass percentage of the first active material in the first coating is greater than the mass percentage of the second active material in the second coating. In the event of an internal short circuit, the short-circuit resistance between the battery cell and the negative electrode can be increased, the short-circuit current can be reduced, and fire can be prevented, thereby increasing the safety performance of the battery cell.

[0007] According to some embodiments of the present invention, the second coating further includes a conductive agent and an adhesive, wherein the second active substance accounts for 70% to 95% of the mass percentage of the second coating, the conductive agent accounts for 3% to 20% of the mass percentage of the second coating, and the adhesive accounts for 1% to 10% of the mass percentage of the second coating.

[0008] According to some embodiments of the present invention, the first coating further includes a conductive agent and an adhesive, wherein the first active substance accounts for 95% to 99.2% of the mass of the first coating, the conductive agent accounts for 0.4% to 2.50% of the mass of the first coating, and the adhesive accounts for 0.4% to 2.50% of the mass of the first coating.

[0009] According to some embodiments of the present invention, the activity of the first active substance is greater than that of the second active substance.

[0010] According to some embodiments of the present invention, the second active material is selected as one or a combination of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium manganese oxide.

[0011] According to some embodiments of the present invention, the thickness of the first coating is between 20 μm and 100 μm.

[0012] According to some embodiments of the present invention, the ratio of the length of the first positive electrode to the length of the second positive electrode is between 2:3 and 4:1 along the winding direction.

[0013] According to some embodiments of the present invention, a third coating is further coated on both sides of the second positive electrode sheet along the thickness direction on the second coating. The third coating includes a third active material, and the mass percentage of the third active material in the third coating is greater than the mass percentage of the second active material in the second coating.

[0014] According to some embodiments of the present invention, the sum of the thickness of the third coating (D2) and the thickness of the second coating (D1) is equal to the thickness of the first coating (H1).

[0015] According to some embodiments of the present invention, the thickness of the second coating is 2µm to 10µm, and the thickness of the third coating is 20µm to 90µm.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0018] Figure 1 This is a schematic diagram of a battery cell according to an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the first positive electrode sheet according to an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of the second positive electrode sheet in an embodiment of the present invention.

[0021] Figure label:

[0022] Positive electrode assembly 100, first positive electrode 110, first coating 111, first current collector 112, second positive electrode 120, second coating 121, third coating 122, second current collector 123;

[0023] Negative electrode plate 200, tab 300, diaphragm 400. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0025] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0026] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0027] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0028] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0029] Reference Figures 1 to 3 The first aspect of the present invention provides a battery cell, including a positive electrode assembly 100, a separator 400 and a negative electrode 200 arranged sequentially along the thickness direction of the battery cell. The positive electrode assembly 100 includes a first positive electrode 110 and a second positive electrode 120 arranged at intervals along the winding direction. Along the thickness direction of the battery cell, at least a portion of the second positive electrode 120 is located outside the first positive electrode 110. At least one tab 300 is provided on the first positive electrode 110, the second positive electrode 120 and the negative electrode 200 respectively.

[0030] The first positive electrode 110 includes a first current collector 112, and a first coating 111 is applied to both sides of the first current collector 112. The second positive electrode 120 includes a second current collector 123, and a second coating 121 is applied to both sides of the second current collector 123. The first coating 111 includes a first active material, and the second coating 121 includes a second active material. The mass percentage of the first active material in the first coating 111 is greater than the mass percentage of the second active material in the second coating 121.

[0031] When the battery cell is in use, independent charging and discharging systems are formed between the first positive electrode 110 and the negative electrode 200, and between the second positive electrode 120 and the negative electrode 200. During discharge, the two systems can output simultaneously to achieve high-rate discharge. Compared with using two single battery cells, the energy density and consistency are improved, solving the problems of single battery cells being unable to maintain high-voltage discharge for a long time and poor rate performance. At the same time, the second positive electrode 120 at least partially covers the outside of the first positive electrode 110. The first positive electrode 110 is coated with a first coating 111 on both sides, and the second positive electrode 120 is coated with a second coating 121 on both sides. The mass percentage of the first active material in the first coating 111 is greater than the mass percentage of the second active material in the second coating 121. The first coating 111 is a normal coating, and the second coating 121 is a safety coating. In the event of an internal short circuit, it can increase the short-circuit resistance between the battery cell and the negative electrode, reduce the short-circuit current, and prevent fire, thereby increasing the safety performance of the battery cell.

[0032] Specifically, the test results regarding the safety performance of the battery cells are shown in the table below:

[0033]

[0034] It can be seen that, compared with ordinary cells, the results of thermal abuse performance tests and nail penetration performance tests of ordinary cells during high-rate discharge are far inferior to those of the cells provided in this application. That is, ordinary cells can meet the safety requirements of thermal abuse performance tests and nail penetration performance tests at low-rate discharge, but their safety is greatly reduced during high-rate discharge. In contrast, the cells provided in this application can achieve a smaller overall temperature rise during high-rate discharge and can basically pass the thermal abuse performance tests and nail penetration performance tests, thus meeting the safety requirements of the cells during high-rate discharge.

[0035] In addition, since the battery cell will generally catch fire the moment the test needle penetrates it if it fails to meet safety requirements during the needle penetration test, the second positive electrode 120 is at least partially covered by the first positive electrode 110. This can prevent instantaneous fire caused by puncturing the covered area of ​​the second positive electrode 120 and improve the safety performance of the battery cell.

[0036] In some embodiments, the second coating 121 further includes a conductive agent and a binder. The second active material accounts for 70% to 95% of the mass percentage of the second coating 121, the conductive agent accounts for 3% to 20% of the mass percentage of the second coating 121, and the binder accounts for 1% to 10% of the mass percentage of the second coating 121. Compared to the coating on a conventional electrode, the second coating 121 has a higher mass percentage of conductive agent and binder, while the mass percentage of active material is reduced. This increases the resistivity of the second coating 121, which can increase the short-circuit resistance between the second coating and the negative electrode, reduce the short-circuit current, and prevent fire in the event of an internal short circuit, thereby increasing the safety performance of the battery cell.

[0037] In some embodiments, the first coating 111 further includes a conductive agent and an adhesive. The first active substance accounts for 95% to 99.2% of the mass of the first coating 111, the conductive agent accounts for 0.4% to 2.50% of the mass of the first coating 111, and the adhesive accounts for 0.4% to 2.50% of the mass of the first coating 1121. Specifically, the active substance of the first coating 111 includes at least one of LiCoO2, LiNiO2, LiMnO4, LiCo1-yMyO2, LiNi1-yMyO4, and LiNixCoyMnzM1-xy-zO2, wherein M is selected from at least one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and 0≤y≤1, 0≤x<1, 0≤z≤1, x+y+z≤1. Non-limiting examples of the adhesive include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, and carboxylated... Polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, single-arm carbon nanotube, multi-arm carbon nanotube, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0038] In some embodiments, the activity of the first active material is greater than that of the second active material. The second active material is selected from one or more combinations of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium manganese oxide. These substances have lower activity and therefore better safety performance.

[0039] In some embodiments, the length ratio of the first positive electrode 110 to the length of the second positive electrode 120 along the winding direction is between 2:3 and 4:1. The lengths of the first positive electrode 110 and the second positive electrode 120 can be determined according to actual usage to meet the performance requirements of the two electrochemical systems, such as the charge-discharge performance and capacity requirements of the two electrochemical systems.

[0040] Reference Figure 3In some embodiments, a third coating 122 is further coated on both sides of the second positive electrode 120 along the thickness direction on the second coating 121. The third coating 122 includes a third active material, and the mass percentage of the third active material in the third coating 122 is greater than the mass percentage of the second active material in the second coating 121. The second positive electrode 120 is coated with a normal coating outside the safety coating, which improves the capacity of the corresponding charge-discharge system while ensuring the safety of the battery cell.

[0041] Specifically, the types and mass percentages of the third active material, conductive agent and adhesive used in the third coating 122 can be exactly the same as those in the first coating 111. The third coating 122 can be applied directly after the second coating 121 is applied, without the need to change the coating materials, thus reducing the processing difficulty.

[0042] Reference Figure 2 and Figure 3 Furthermore, the sum of the thickness (D2) of the third coating 122 and the thickness (D1) of the second coating 121 is equal to the thickness of the first coating 111 (H1). Both the first positive electrode 110 and the second positive electrode 120 are rolled to the same thickness after coating with the slurry to ensure the overall consistency of the battery cell after winding with the separator 400 and the negative electrode 200. Specifically, the thickness of the first coating 111 is between 20µm and 100µm, the thickness of the second coating 121 is between 2µm and 10µm, and the thickness of the third coating 122 is between 20µm and 90µm. The thickness of each coating can be selected according to actual conditions, and will not be elaborated further here.

[0043] Reference Figure 1 In some embodiments, the first positive electrode 110, the second positive electrode 120, and the negative electrode 200 are each provided with one or more tabs 300. The tabs 300 are connected to the empty foil area of ​​each electrode. The empty foil area can be located at the end of the electrode along the winding direction or at the middle of the electrode. The tabs 300 provided on the first positive electrode 110 and the second positive electrode 120 correspond to the tabs 300 provided on the negative electrode 200, which can realize the charging and discharging of the battery cell.

[0044] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A battery cell, characterized in that, The battery cell includes a positive electrode assembly, a separator, and a negative electrode assembly arranged sequentially along the thickness direction of the battery cell. The positive electrode assembly includes a first positive electrode and a second positive electrode arranged at intervals along the winding direction. Along the thickness direction of the battery cell, at least a portion of the second positive electrode covers the outside of the first positive electrode. At least one tab is provided on each of the first positive electrode, the second positive electrode, and the negative electrode assembly. The first positive electrode includes a first current collector, and a first coating is applied to both sides of the first current collector. The second positive electrode includes a second current collector, and a second coating is applied to both sides of the second current collector. The first coating includes a first active material, and the second coating includes a second active material. The mass percentage of the first active material in the first coating is greater than the mass percentage of the second active material in the second coating. The first positive electrode and the second positive electrode are independent of each other and can form independent charging and discharging systems with the negative electrode, respectively.

2. The battery cell according to claim 1, characterized in that, The second coating further includes a conductive agent and an adhesive, wherein the second active substance accounts for 70% to 95% of the mass of the second coating, the conductive agent accounts for 3% to 20% of the mass of the second coating, and the adhesive accounts for 1% to 10% of the mass of the second coating.

3. The battery cell according to claim 1 or 2, characterized in that, The first coating further includes a conductive agent and an adhesive, wherein the first active substance accounts for 95% to 99.2% of the mass of the first coating, the conductive agent accounts for 0.4% to 2.50% of the mass of the first coating, and the adhesive accounts for 0.4% to 2.50% of the mass of the first coating.

4. The battery cell according to claim 1, characterized in that, The activity of the first active substance is greater than that of the second active substance.

5. The battery cell according to claim 4, characterized in that, The second active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium manganese oxide.

6. The battery cell according to claim 1, characterized in that, The thickness of the first coating is between 20um and 100um.

7. The battery cell according to claim 1, characterized in that, Along the winding direction, the ratio of the length of the first positive electrode to the length of the second positive electrode is between 2:3 and 4:

1.

8. The battery cell according to claim 1, characterized in that, The second positive electrode sheet is further coated with a third coating on both sides of the second coating along the thickness direction. The third coating includes a third active material, and the mass percentage of the third active material in the third coating is greater than the mass percentage of the second active material in the second coating.

9. The battery cell according to claim 8, characterized in that, The sum of the thickness of the third coating (D2) and the thickness of the second coating (D1) is equal to the thickness of the first coating (H1).

10. The battery cell according to claim 9, characterized in that, The thickness of the second coating is 2µm to 10µm, and the thickness of the third coating is 20µm to 90µm.

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