A positive electrode sheet and a cylindrical lithium-ion battery containing the same

Abstract

The present invention provides a positive electrode plate and a cylindrical lithium-ion battery containing the same. The positive electrode plate includes a current collector and one or more tabs; the surface of the current collector is provided with an active material layer and one or more blank areas; any of the tabs includes an upper end portion for welding and fixing to a metal cover plate; and a lower end portion for welding and fixing to the blank area of ​​the current collector; the bottom end of the upper end portion and the top end of the lower end portion are connected and fixed; the shape of the upper end portion and the lower end portion are both rectangular, the width of the rectangle where the upper end portion is located is L3, the width of the rectangle where the lower end portion is located is L2, and L3 is greater than L2. The positive electrode plate increases the welding area between the positive electrode tab and the top cover of the cylindrical battery cell, improves and increases the overcurrent capacity, and prevents lithium deposition and material shedding caused by heat.

Description

Technical Field

[0001] The present invention belongs to the technical field of positive electrode sheets for cylindrical batteries, and in particular relates to a positive electrode sheet and a cylindrical lithium-ion battery containing the same. Background Art

[0002] Various battery configurations include prismatic, button-shaped, and cylindrical. In a cylindrical battery configuration, the positive electrode, separator, and negative electrode are wound around a center pin to form a cylinder. The positive and negative electrode sheets are electrically connected to the outside world through tabs.

[0003] Currently, cylindrical steel-shell power lithium batteries are constructed with single-pole tabs and bipolar tabs, both of which are rectangular in shape. Under normal circumstances, when lithium batteries undergo power testing, the current is large and the heat generated is relatively large, which causes a thermal reaction inside the battery cell and produces gas, resulting in pole piece falling off, lithium deposition, CID flipping, and other phenomena. Summary of the Invention

[0004] In order to overcome the problems of existing cylindrical lithium batteries undergoing high-rate testing, such as severe heat generation leading to lithium deposition and material shedding, the present invention provides a positive electrode sheet and a cylindrical lithium-ion battery comprising the same.

[0005] Specifically, the present invention provides the following technical solutions:

[0006] A positive electrode sheet for a cylindrical lithium-ion battery, comprising a current collector and one or more tabs; an active material layer and one or more blank areas are provided on the surface of the current collector;

[0007] Any of the tabs includes an upper end portion for welding and fixing to the metal cover plate; and a lower end portion for welding and fixing to the blank area of ​​the current collector; the bottom end of the upper end portion and the top end of the lower end portion are connected and fixed;

[0008] The upper end and the lower end are both rectangular in shape. The width of the rectangle where the upper end is located is L3, and the width of the rectangle where the lower end is located is L2. L3 is greater than L2.

[0009] Preferably, in the above-mentioned positive electrode sheet, L2<L3<(3×L2). When L3≥(3×L2), the current overflow time is longer during normal charge and discharge of the battery cell, and the heat generation increases, thereby affecting the heat dissipation of the battery cell and possibly causing the battery cell to fail.

[0010] More preferably, L3 is (1.8×L2) to (2.2×L2). The present invention has found that limiting the size relationship between L3 and L2 to the above range can significantly improve the heat generation.

[0011] Preferably, the above-mentioned positive electrode sheet comprises two tabs spaced apart along the length of the current collector, and the surface of the current collector is provided with two blank areas spaced apart along the length of the current collector and connected to the tabs.

[0012] Preferably, in the above-mentioned positive electrode sheet, the width L2 of the rectangle in which the lower end of any of the tabs is located is 0.4-0.6% of the length of the current collector. If L2 is less than 0.4% of the current collector length, it will affect the welding area between the lower end of the tab and the current collector; if L2 is greater than 0.6% of the current collector length, it will affect the winding formation of the current collector.

[0013] Preferably, in the above-mentioned positive electrode sheet, the shape of any of the blank areas is a rectangle, the width of the rectangle where the blank area is located is L1, and L1 is greater than L2.

[0014] Preferably, in the above-mentioned positive electrode sheet, the unit of L2 is mm, and the area of ​​the rectangle where the lower end of the tab sheet is exposed to the current collector is (3×L2) to (5×L2) mm. 2 The portion of the lower end of the tab that is exposed from the current collector is the bent section of the tab. If the exposed area of ​​the rectangle where the lower end is located is too small, the lower left and lower right corners of the rectangle where the upper end is located will collide with the battery core when the tab is bent. If the exposed area of ​​the rectangle where the lower end is located is too large, the welding area between the bent tab and the metal cover will be reduced, thereby reducing the flow capacity and increasing the temperature rise.

[0015] Preferably, in the above-mentioned positive electrode sheet, the upper end of the electrode tab is fixed to the metal cover plate by ultrasonic welding; and the lower end of the electrode tab is fixed to the blank area of ​​the current collector by ultrasonic welding.

[0016] Preferably, in the above-mentioned positive electrode sheet, the material of the current collector is aluminum foil with a thickness of 10 to 20 μm;

[0017] And / or, the tab is made of aluminum with a thickness of 0.1 to 0.5 mm;

[0018] And / or, the active material layer includes a positive electrode active material, a binder and a conductive agent; further preferably, in the active material layer, the amount of the positive electrode active material is 90-97wt%, the amount of the binder is 0.5-3wt%, and the amount of the conductive agent is 0-6wt%.

[0019] The present invention also provides a cylindrical lithium-ion battery, comprising the above-mentioned positive electrode plate, a separator, an electrolyte and a negative electrode plate.

[0020] The beneficial effects achieved by the present invention are:

[0021] The positive electrode sheet for a cylindrical lithium-ion battery provided by the present invention has a blank area on the surface of the current collector, and the other area is the active material area. The positive electrode tab sheet is shaped like two rectangles of different sizes combined into one. The small rectangle is ultrasonically welded to the blank area, and the large rectangle is ultrasonically welded to the cover plate of the cylindrical battery. This will increase the welding area between the positive electrode tab sheet and the top cover of the cylindrical battery cell, improve and increase the current flow capacity, and prevent lithium precipitation and material falling due to heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the positive electrode plate structure of Example 1, wherein 1-pole tab, 2-current collector, 3-blank area.

[0023] Figure 2 The temperature rise comparison of the battery cells made with the positive electrode sheets provided by Example 1 and Comparative Example 1 at different discharge rates is shown. DETAILED DESCRIPTION

[0024] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or the product instructions were used.

[0025] Example 1

[0026] like Figure 1 As shown, embodiment 1 provides a positive electrode sheet, including a current collector and two tabs spaced along the length of the current collector;

[0027] The current collector is made of aluminum foil, with a length of 2100 mm, a height of 58 mm, and a thickness of 15 μm. The surface of the current collector is provided with two blank areas spaced equidistantly along the length of the current collector and connected to the tabs, and the remaining area is the active material layer.

[0028] Any of the blank areas is a rectangle, and the width L1 of the rectangle where the blank area is located is 10.5 mm and the height is 58 mm;

[0029] The active material layer includes 91 wt% of the positive electrode active material (the positive electrode active material is a ternary material), 3 wt% of the binder (PVDF), 4.5 wt% of the conductive agent Super-P, and 1.5 wt% of the carbon nanotubes.

[0030] Any of the tabs is made of aluminum and has a thickness of 0.5 mm. It includes an upper end for ultrasonically welding the cover of the cylindrical battery and a lower end for ultrasonically welding the blank area of ​​the current collector.

[0031] The upper end and the lower end are both rectangular in shape, the width L3 of the rectangle where the upper end is located is 16 mm and the height is 27 mm, and the width L2 of the rectangle where the lower end is located is 8 mm and the height is 61 mm;

[0032] The area of ​​the rectangle where the lower end of the tab is exposed to the current collector is (4×L2) mm 2 .

[0033] The preparation steps are as follows: the powders of the positive electrode active material, binder and conductive agent and the solvent are homogenized (a total of 7 hours of homogenization process), and dispersed to make a positive electrode slurry. The positive electrode slurry is coated on the surface of the positive electrode collector using an interval coating method. The uncoated area is the blank area. After coating is completed, it is rolled and cut, and the positive electrode tab is ultrasonically welded in the blank area to obtain the positive electrode sheet.

[0034] The obtained positive electrode sheets are assembled, and after the positive and negative electrode sheets are ultrasonically welded to the tabs, they are wound with the diaphragm, and a roll core is rolled out. The roll core is placed in the shell, and the bottom is tapped, grooved, baked, and liquid-injected. After liquid injection, the upper end of the tab sheet is ultrasonically welded to the cover of the cylindrical battery, and then sealed to make a battery cell.

[0035] Comparative Example 1

[0036] The only difference between Comparative Example 1 and Example 1 is that the width of the upper end of the tab is 8 mm, which is the same as the width of the lower end.

[0037] Comparative Example 2

[0038] The only difference between Comparative Example 2 and Example 1 is that the area of ​​the rectangle where the lower end of the tab is exposed to the current collector is 2×L2mm. 2 .

[0039] Comparative Example 3

[0040] The only difference between Comparative Column 3 and Example 1 is that the area of ​​the rectangle where the lower end of the tab is exposed to the current collector is 6×L2mm. 2 .

[0041] Test example

[0042] 1. Battery cell manufacturing process

[0043] The cell manufacturing results for Example 1 and Comparative Examples 1-3 are shown in Table 1 below. The post-winding short-circuit rate data was obtained using a short-circuit tester, where two positive and negative probes were placed in contact with the positive and negative electrodes of the winding core. Fifty samples were tested for each example. Specifically, after winding, each sample was short-circuited, and the number of samples that shorted was recorded. The remaining samples were then shelled, bottomed, and grooved, and then short-circuited again. The number of samples that shorted was also recorded. The short-circuit rate was calculated by summing the two short-circuited sample counts.

[0044] Table 1

[0045] Short circuit rate after winding Welding of the tab and cover Close the lid in conclusion Example 1 0％ Weldable Closable lid Producible Comparative Example 1 0％ Weldable Closable lid Producible Comparative Example 2 10％ Weldable Closable lid Unable to produce Comparative Example 3 0％ Weldable Unable to close the lid Unable to produce

[0046] The reason for the high short-circuit rate in comparative example 2 is that during the shell insertion and bending process of the tab, the lower left and left and right sharp corners of the upper end of the tab will puncture the diaphragm of the winding core, causing a short circuit.

[0047] The reason why the comparative example 3 cannot be closed is that during the bending process of the tab, the bent tab contacts the inside of the shell and cannot be closed.

[0048] 2. Battery cell testing

[0049] The cells made of the positive electrodes of Example 1 and Comparative Example 1 were discharged at different rates and the temperature rise was compared. Figure 2 As shown, the vertical axis temperature is the maximum temperature minus the minimum temperature.

[0050] like Figure 2 From the results shown, the temperature rise of Example 1 is lower than that of Comparative Example 1, and the 10C rate test can be performed, while Comparative Example 1 cannot perform the 10C rate test. The reason is that during the test of Comparative Example 1, severe heat is generated and the gas production is large, causing the battery cell structure to fail (CID flip), and the voltage will drop to 0V.

[0051] Although the present invention has been described in detail above using general explanations, specific embodiments, and experiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A positive electrode sheet for a cylindrical lithium-ion battery, characterized in that: It includes a current collector and one or more tabs; the surface of the current collector is provided with an active material layer and one or more blank areas; Any of the tabs includes an upper end portion for welding and fixing to the metal cover plate; and a lower end portion for welding and fixing to the blank area of ​​the current collector; the bottom end of the upper end portion and the top end of the lower end portion are connected and fixed; The upper end and the lower end are both rectangular in shape, the width of the rectangle where the upper end is located is L3, the width of the rectangle where the lower end is located is L2, and L3 is (1.8×L2) to (2.2×L2); The unit of L2 is mm, and the area of ​​the rectangle where the lower end of the tab is exposed to the current collector is (3×L2)~(5×L2) mm 2 .

2. The positive electrode sheet for a cylindrical lithium-ion battery according to claim 1, characterized in that: It comprises two tabs spaced apart along the length of the current collector, and the surface of the current collector is provided with two blank areas spaced apart along the length of the current collector and connected to the tabs.

3. The positive electrode sheet for a cylindrical lithium-ion battery according to claim 1, characterized in that: The width L2 of the rectangle where the lower end of any of the tabs is located is 0.4-0.6% of the length of the current collector.

4. The positive electrode sheet for a cylindrical lithium-ion battery according to claim 1, characterized in that: Any of the blank areas is a rectangle, the width of the rectangle where the blank area is located is L1, and L1 is greater than L2.

5. The positive electrode sheet for a cylindrical lithium-ion battery according to claim 1, characterized in that: The upper end of the pole tab is fixed to the metal cover plate by ultrasonic welding; the lower end of the pole tab is fixed to the blank area of ​​the current collector by ultrasonic welding.

6. The positive electrode sheet for a cylindrical lithium-ion battery according to claim 1, characterized in that: The material of the current collector is aluminum foil with a thickness of 10-20 μm; And / or, the tab is made of aluminum with a thickness of 0.1-0.5 mm; And / or, the active material layer includes a positive electrode active material, a binder and a conductive agent.

7. The positive electrode sheet for a cylindrical lithium-ion battery according to claim 6, characterized in that: In the active material layer, the amount of the positive electrode active material is 90-97 wt %, the amount of the binder is 0.5-3 wt %, and the amount of the conductive agent is 0-6 wt %.

8. A cylindrical lithium-ion battery, characterized in that: The invention comprises the positive electrode sheet, the separator, the electrolyte and the negative electrode sheet according to any one of claims 1 to 7.

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