Composite pole piece and full-tab high-nickel cylindrical battery cell passing acupuncture test at lower temperature

Abstract

The utility model discloses a composite pole piece and a full-tab high-nickel cylindrical battery cell passing a needling test at a lower temperature, the composite pole piece comprises foil layers, a macromolecule base film layer, an electrode slurry layer and a welding foil layer, the two end surfaces of the macromolecule base film layer are respectively provided with one foil layer, and the electrode slurry layer is provided with one welding foil layer. An electrode slurry layer and an empty foil area are arranged on the working end face of the foil layer; the welding end of the welding foil layer is welded to the empty foil area, and the free end of the welding foil layer exceeds the foil layer and is exposed out of the foil layer. According to the utility model, the structure of the battery cell pole piece is changed, the composite aluminum foil is used as a base material, the two end surfaces of the composite aluminum foil are coated with the positive active material, and the empty foil area of the composite aluminum foil is welded with the common aluminum foil extension tab area; after the cell is punctured, the local current density is sharply increased, so that the temperature of a punctured point rises, the macromolecular base film layer is melted and shrunk, and the metal coating on the macromolecular base film layer is pulled away from a punctured body to form a physical isolation strip, so that the short-circuit resistance is improved to a kiloohm level, the short-circuit current is inhibited, and the needling passing rate of the cell is improved.

Description

Technical Field

[0001] This utility model belongs to the field of lithium battery needle penetration, specifically relating to a composite electrode sheet and a full-tab high-nickel cylindrical cell that passes the needle penetration test at a lower temperature. Background Technology

[0002] Against the backdrop of the global energy structure's accelerated transition to cleaner energy, lithium-ion batteries, as the core technology carrier of the new energy revolution, have made performance optimization a key issue for industrial development. The current market's continuously upgrading demand for battery energy density is driving the evolution of cathode material systems towards higher nickel content. However, there is a significant negative correlation between increasing the nickel content in materials and their thermodynamic stability. This technical contradiction is becoming increasingly prominent with the introduction of mandatory needle penetration testing for power batteries in new national standards.

[0003] When a high-nickel lithium battery cell is punctured by a sharp object, the mechanical damage from the external force directly triggers an internal short circuit. At the instant the short circuit forms, the current violently releases energy along the abnormal path, causing an exponential accumulation of heat within the cell. Due to the inherent thermal stability defects of the high-nickel ternary cathode material, it rapidly undergoes crystal structure recombination at high temperatures, with oxygen atoms in the layered oxide lattice beginning to precipitate in large quantities under lattice distortion. These free oxygen molecules undergo a violent oxidation reaction with the organic solvent in the electrolyte, simultaneously catalyzing the decomposition of the cathode active material and releasing additional heat. This energy release and temperature rise form a self-sustaining exothermic chain reaction, causing the cell to exceed the thermal runaway critical temperature threshold within seconds. The resulting violent exothermic process leads to a chain reaction of failures, such as electrolyte vaporization and separator melting, causing the battery system to produce jet flames or deflagration under extreme conditions. This poses a serious safety hazard to applications in enclosed spaces, such as new energy vehicles, potentially limiting the mainstream applications of high-nickel ternary batteries due to their inability to meet extreme safety testing requirements. Utility Model Content

[0004] This invention provides a composite electrode sheet and a high-nickel cylindrical battery cell with all tabs that passes the needle penetration test at a lower temperature. It changes the structure of the high-nickel cylindrical battery cell from a structural perspective and improves its needle penetration pass rate.

[0005] The technical solution adopted in this utility model is as follows:

[0006] A composite electrode sheet includes a composite foil sheet, an electrode paste layer, and a welding foil layer. The composite foil sheet comprises a foil layer and a polymer base film layer. A foil layer is provided on each of the two ends of the polymer base film layer. The end of the foil layer away from the polymer base film layer is the working end face. An electrode paste layer and an empty foil area are provided on the working end face, with the empty foil area located on the side of the working end face. The welding end of the welding foil layer is welded to the empty foil area, and the free end of the welding foil layer protrudes beyond the foil layer. There is a gap between the welding end of the welding foil layer and the electrode paste layer to avoid damage to the electrode paste layer during welding. When a composite electrode is used for the positive electrode, aluminum foil is used for the foil layer, and the corresponding welding foil layer is also aluminum foil. Positive electrode paste is used as the electrode slurry, which is coated onto the foil layer to form the positive electrode slurry layer. The uncoated areas are the empty foil areas. Ordinary aluminum foil is used for the welding foil layer, and its length is the same as the length of the empty foil areas, ensuring complete coverage of the empty foil areas. The width of the welding foil layer exceeds the width of the empty foil areas, where roll welding is used. The welding foil layer serves as an extension of the empty foil areas within the same composite electrode. The two welding foil layers together with the corresponding empty foil area serve as the total tab of the composite electrode. Since the base film in the middle of the composite foil sheet is a polymer base film, such as PET or PP, the empty foil area of ​​the composite foil sheet cannot be used to weld the current collector directly. Direct welding would cause the polymer base film to melt due to the welding temperature, resulting in insufficient strength. Therefore, roll welding of the foil layer is required. Similarly, when the negative electrode sheet uses a composite electrode sheet, the foil layer is made of copper foil, the corresponding welding foil layer is ordinary copper foil, and the electrode paste is negative electrode paste.

[0007] In a preferred embodiment of this invention, the polymer base film layer is a PE film, a PET film, or a PP film.

[0008] In a preferred embodiment of this invention, the thickness of the polymer base film layer is 4-8 μm; the thickness of the foil layer is 1-2 μm.

[0009] This utility model also provides a high-nickel cylindrical battery cell with all tabs that passes the needle penetration test at a lower temperature, comprising a positive electrode, a negative electrode, and a separator. The positive electrode is the aforementioned composite electrode, and the negative electrode can be either a regular negative electrode or the aforementioned composite electrode. Because the needle penetration test of the battery cell is equivalent to a direct internal short circuit, there are four main modes of internal short circuits in a battery: Mode 1: short circuit between the positive and negative electrode active materials, i.e., a short circuit between the positive and negative electrode slurry layers; Mode 2: short circuit between the negative electrode current collector and the positive electrode active material; Mode 3: short circuit between the positive and negative electrode current collectors; Mode 4: short circuit between the positive electrode current collector and the negative electrode active material. Mode 3 will result in arcing, and Mode 4 will result in a fire, both of which are dangerous situations. Therefore, the improvement mainly targets the positive electrode of the battery cell.

[0010] This invention modifies the electrode structure of the battery cell, especially the positive electrode. It uses composite aluminum foil as the substrate, and positive active material is coated on both ends of the composite aluminum foil. In order to adapt to the full tab structure, ordinary aluminum foil is welded to the empty foil area of ​​the composite aluminum foil to extend the tab area. When the battery cell made of composite foil structure is punctured, the temperature of the puncture point rises due to the surge in local current density. The polymer base film layer in the composite foil melts and shrinks. The shrinkage of the polymer base film layer will pull the metal coating on it away from the puncture body, forming a physical isolation zone, which increases the short-circuit resistance to the kiloohm level, suppresses the short-circuit current, and improves the battery cell needle penetration rate. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of the composite positive electrode structure.

[0013] Figure 2 This is a schematic diagram of the composite negative electrode.

[0014] Figure 3 This is a schematic diagram illustrating the principle of needle puncture breaking in a battery cell where both the positive and negative electrodes are composite electrodes.

[0015] Figure 4 This is a sample of a needle-punctured battery cell. Detailed Implementation

[0016] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0017] Example 1:

[0018] A composite electrode includes a composite foil sheet 1, an electrode paste layer 2, and a welding foil layer 3. This embodiment uses a positive electrode sheet as an example. Figure 1 As shown, the composite foil sheet 1 includes a foil layer 11 and a polymer base film layer 12. The foil layer 11 is an aluminum foil layer with a thickness of 1-2 μm; the polymer base film layer 12 is a PE film, PET film or PP film with a thickness of 4-8 μm.

[0019] Aluminum foil is coated on both ends of the polymer base film layer 12 to form foil layers 11. The end face of each foil layer 11 away from the polymer base film layer 12 is the working end face. An electrode paste layer 2 and an empty foil area 131 are provided on the working end face. Here, the electrode paste layer 2 is coated with positive electrode active material, and the area on the same working end face that is not coated with positive electrode active material is the empty foil area. The empty foil area 131 is located on the side of the working end face.

[0020] The welding foil layer 3 uses ordinary aluminum foil. One end of the welding foil layer 3 is placed in the empty foil area of ​​the corresponding foil layer and serves as the welding end. The welding end is welded to the empty foil area 131 using a roll welding method. The other end of the welding foil layer is a free end, which extends away from the foil layer and protrudes beyond the foil layer 11. The length of the welding foil layer is the same as the length of the empty foil area, which can cover the entire empty foil area with the welding foil layer.

[0021] To avoid affecting the positive electrode active material during roll welding or welding with the positive electrode current collector, a gap is made between the welding end of the welding foil layer 3 and the electrode slurry layer 2.

[0022] The composite electrode has two foil layers 11, so each foil layer 11 has a welded foil layer 3 welded to its empty foil area. The two welded foil layers 3 and the corresponding empty foil areas together form the full tab area of ​​the composite electrode.

[0023] Example 2:

[0024] A composite negative electrode, such as Figure 2 As shown, the foil layer uses copper foil, the welding foil layer uses copper foil, and the electrode paste layer 2 is coated with a negative electrode active material. The rest are the same as in Example 1.

[0025] Example 3:

[0026] A high-nickel cylindrical battery cell with all tabs that passes a needle penetration test at a relatively low temperature includes a positive electrode 4, a negative electrode 5, and a separator 6. The positive electrode 4 adopts the composite electrode shown in Example 1. Figure 1 As shown, the negative electrode uses the composite electrode from Example 2, such as... Figure 2 As shown, the positive electrode, separator, and negative electrode are wound together to form a battery cell, with the welding foil layer 3 of the positive electrode facing one side of the battery cell and the welding foil layer 3 of the negative electrode facing the other side of the battery cell. The polymer base film layer of the composite electrode will melt and shrink at high temperature, pulling the metal coating on the polymer base film layer away from the puncture body to form a physical isolation zone.

[0027] When the battery cell is punctured by the puncture body 7, firstly, the local current density of the battery cell surges to 10^3 times that under normal operating conditions. The Joule heating effect causes the temperature at the puncture point to rise at a rate greater than 50℃ / s to the critical point of 120-150℃. This stage is the thermal trigger response stage. Secondly, the polymer base film layer of the composite electrode melts and shrinks at high temperature. This stage is the heating stage. Thirdly, the shrinkage of the polymer base film layer causes the aluminum foil layer or copper foil layer to be pulled apart, forming a physical isolation band greater than 200μm between the positive and negative electrode plates and the puncture body. This causes the short-circuit resistance to jump from the milliohm level to the kilohm level, effectively suppressing the short-circuit current to below 10mA / cm². The puncture diagram is shown below. Figure 3 As shown, this stage is the physical isolation stage; finally, the entire process can cut off the continuous heat generation path within 300ms, so that the thermal runaway triggering conditions cannot be met, and the thermal runaway blocking stage can be achieved, which can improve the needle penetration pass rate of high-nickel cylindrical cells.

[0028] To verify the effectiveness of this application, experimental examples and comparative examples are provided below.

[0029] Prepare positive and negative electrode slurries:

[0030] ① Select nickel-cobalt-manganese ternary material (LiNixCoyMn1-x-yO2). To ensure the energy density of the battery cell, the proportion of X is greater than 0.8. Then add lithium iron phosphate manganese to mix, mainly to improve the thermal stability of the material.

[0031] The negative electrode uses a conventional silicon-oxygen + graphite combination with cell raw materials such as SP and PVDF, and is made into a paste in a certain proportion.

[0032] Preparation of positive and negative electrodes:

[0033] ① The positive electrode paste is coated onto the composite aluminum foil, and ordinary aluminum foil is rolled onto the composite aluminum foil to prepare electrode A; the positive electrode paste is coated onto the aluminum foil to prepare electrode C;

[0034] ② The negative electrode paste is coated onto the composite copper foil, and ordinary copper foil is rolled onto the composite copper foil to prepare electrode B; the negative electrode paste is coated onto the copper foil to prepare electrode D.

[0035] Battery cell prototype manufacturing:

[0036] Option 1:

[0037] Electrode A is wound together with electrode B and separator to form a cell; the separator is an alumina-coated separator, which is then installed in the housing to form an experimental cylindrical cell, electrolyte is injected, and experimental cylindrical batteries are obtained through formation and aging processes.

[0038] Option 2:

[0039] Electrode C is wound together with electrode D and separator to form a battery cell. The separator is an alumina-coated separator. Then, it is installed in the housing to form a comparative cylindrical battery cell. Electrolyte is injected, and a comparative cylindrical battery is obtained through formation and aging processes.

[0040] The experimental lithium-ion battery and the control lithium-ion battery were subjected to nail penetration tests. The results are shown in the table below, and the sample photograph of Scheme 1 is shown in the image below. Figure 4 As shown in the table below, the results of acupuncture are as follows:

[0041]

[0042] Moreover, it still has a high voltage after being punctured, and the highest temperature of the battery cell is only about 40°C.

[0043] Example 4:

[0044] A high-nickel cylindrical battery cell with all tabs that passes the needle penetration test at a lower temperature includes a positive electrode, a negative electrode, and a separator. The positive electrode adopts the composite electrode of Example 1, and the negative electrode adopts the structure of ordinary copper foil coated with negative electrode active material. The rest are the same as in Example 3.

[0045] In this specification, the terms "an embodiment," "example," "specific example," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present 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.

[0046] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A composite pole piece characterized by: The positive electrode sheet (4) is the composite electrode sheet as claimed in any one of claims 1-3.

2. The composite pole piece of claim 1, wherein: The negative electrode sheet (5) is the composite electrode sheet as claimed in any one of claims 1-3.

3. The composite pole piece of claim 1 or 2, wherein: ​ 4. A full tab high nickel cylindrical cell with lower temperature by needle test, comprising a positive electrode sheet (4), a negative electrode sheet (5) and a separator (6), characterized in that: ​ 5. The full tabbed high nickel cylindrical cell passing the lower temperature needle test of claim 4, wherein: ​

Images