High energy density high safety tab-free lithium ion battery

Abstract

The application provides a high-energy-density high-safety tab-free lithium ion battery, which comprises an outer shell and an electric core, and a cover plate is arranged on the top of the outer shell; the electric core is composed of positive electrode sheets and negative electrode sheets which are separated by a diaphragm and are wound; the positive electrode sheets and the negative electrode sheets are respectively designed as wide-width reduced empty foil areas, and the empty foil areas of the positive electrode sheets and the negative electrode sheets form gap areas with intervals on the surface of the electric core through the reduced-width parts after winding, and the positive electrode sheet empty foil areas and the negative electrode sheet empty foil areas are respectively formed on the two sides of the gap areas; the outer shell has shell areas composed of different materials, including a first metal shell area, an insulating connection area and a second metal shell area arranged in sequence, and the positive electrode sheet empty foil areas and the negative electrode sheet empty foil areas of the electric core respectively fall into the first metal shell area and the second metal shell area in the whole, and the insulating connection area falls into the gap area of the electric core. The application greatly improves and improves the energy density and thermal runaway.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-energy-density, high-safety tabless lithium-ion battery. Background Technology

[0002] Currently, lithium-ion batteries can be mainly classified into aluminum-cased batteries, steel-cased batteries, and polymer batteries based on their outer packaging. Depending on the material of the casing, the outer shell of an aluminum-cased battery is the positive electrode, and the rivet position on the cover is the negative electrode; the steel-cased battery is the opposite, with the outer shell being the negative electrode and the rivet position being the positive electrode. Regardless of whether it's a steel-cased or aluminum-cased battery, the battery is connected to the casing and rivets via aluminum and nickel strips leading from the electrode plates. Therefore, current designs and manufacturing require at least 4-5mm of space between the casing and the cover to accommodate the aluminum and nickel strips leading from the positive and negative electrodes. This design often sacrifices a significant amount of energy density for 3C digital batteries with high energy density requirements; for example, if the battery height is 50mm, this sacrifice can result in an 8%-10% reduction in energy density. Similarly, in traditional steel-cased and aluminum-cased batteries, heat transfer within the battery relies solely on the aluminum and nickel strips inside the cell to the casing, and then through the casing to the outside. This slow heat transfer and dissipation rate results in significant thermal runaway risks for traditional aluminum-cased and steel-cased lithium-ion batteries. For polymer pouch batteries, the casing is made of non-metallic materials, and both the positive and negative electrodes are led out via tabs. The welding of these tabs and the application of adhesive for external cell protection contribute to long production cycles and high production costs. Furthermore, during laser welding, the aluminum and nickel strips can easily become stuck against the casing and cover, leading to weld defects.

[0003] Some existing battery designs aim to simplify the manufacturing process and structure by removing the tabs. However, while removing the tabs improves performance, it also reduces the reliability of the positive and negative electrode connections. This often leads to problems such as poor electrode contact, impaired current and heat conduction, and a decrease in battery capacity instead of an increase. Therefore, this limits the widespread application of tabless-free battery structures. Summary of the Invention

[0004] This invention addresses the problems in the prior art by designing a high-energy-density, high-safety tabless lithium-ion battery, which achieves significant improvements in both energy density and thermal runaway control.

[0005] Specifically, the high-energy-density, high-safety tabless lithium-ion battery of the present invention includes a battery cell placed inside a housing, and a cover plate is provided on the top of the housing. The battery cell is composed of positive and negative electrode sheets separated by a separator and then wound together. The ends of the positive and negative electrode sheets are designed as empty foil areas with reduced width. After winding, the empty foil areas of the positive and negative electrode sheets form a gap area with spacing on the surface of the battery cell through the reduced width portion, and positive electrode empty foil areas and negative electrode empty foil areas are respectively formed on both sides of the gap area. The housing has a shell area made of different materials, including a first metal shell area, an insulating connection area, and a second metal shell area arranged in sequence. The positive electrode empty foil areas and negative electrode empty foil areas on the battery cell all fall into the first metal shell area and the second metal shell area respectively, and the insulating connection area falls into the gap area of ​​the battery cell.

[0006] The first metal shell area of ​​the outer shell is an aluminum shell, and the second metal shell area is a steel shell.

[0007] The cover plate includes, from top to bottom, a first cover plate, a second cover plate, and a third cover plate. A step is formed between the first cover plate and the second cover plate, which corresponds to the thickness of the outer shell. All the steps are made of aluminum. The third cover plate is an insulating layer.

[0008] Furthermore, an injection hole is also provided on the cover plate.

[0009] The bottom of the battery cell has an insulating protective layer.

[0010] Wherein, the gap A between the top of the battery cell and the bottom surface of the cover plate inside the outer casing is 0.5-6mm; the ratio between the thickness of the battery cell and the thickness of the inner cavity of the outer casing is the fill ratio B, which is 85%-97%; the ratio between the width of the empty foil area of ​​the positive electrode sheet and the width of the empty foil area of ​​the negative electrode sheet is the foil width ratio C, with a specific value of 0.1-9; the ratio between the sum of the widths of the empty foil areas of the positive electrode sheet and the empty foil areas of the negative electrode sheet and the width of the negative electrode load area is the foil occupancy ratio D, with a specific value of 0.9≤Foil Occupancy Ratio D<1.

[0011] Furthermore, the gap A is preferably 1-6mm, more preferably 1.5-6mm, and most preferably 1.5-2.5mm.

[0012] Furthermore, the filling ratio B is preferably 88% to 95%.

[0013] Furthermore, the foil width ratio C is preferably 0.4 to 2.3, more preferably 1 ± 0.5.

[0014] This invention, through innovative battery structure design, enables the battery structure to successfully eliminate the design space of the tabs, effectively improving the energy density of the battery. At the same time, through structural size optimization, it effectively solves the problems that may be caused by the omission of tabs, such as poor contact, reduced safety, temperature resistance and structural changes, ensuring rapid conduction of current and heat under high energy density. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the general structure of a traditional battery with tabs.

[0016] Figure 2 This is a schematic diagram of the positive electrode structure of the present invention.

[0017] Figure 3 This is a schematic diagram of the negative electrode structure of the present invention.

[0018] Figure 4 This is a schematic diagram of the structure of the battery cell after winding according to the present invention.

[0019] Figure 5 This is a schematic diagram of the outer shell of the present invention.

[0020] Figure 6 This is a schematic diagram of the cover plate of the present invention.

[0021] Figure 7 This is a schematic diagram of the internal structure of the battery of the present invention. Detailed Implementation

[0022] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0023] The typical structural design of a traditional battery with tabs is as follows: Figure 1 As shown, the battery cell 3 is placed inside the outer casing 4. The top of the outer casing 4 is a cover plate 5. The top of the battery cell 3 has a positive electrode tab 3-7 and a negative electrode tab 3-8 leading out. A tab connector 5-5 needs to be designed inward on the cover plate 5 for connecting with the positive electrode tab 3-7 and / or the negative electrode tab 3-8. The presence of the two tabs and the tab connector 5-5 greatly occupies the space inside the outer casing 4, resulting in wasted space and a reduction in battery energy density.

[0024] The battery cell 3 of the present invention is composed of positive and negative electrode sheets separated by a separator and then wound together. The ends of the positive and negative electrode sheets are designed as empty foil areas with reduced width. After winding, the empty foil areas of the positive and negative electrode sheets form gap areas 3-4 with spacing on the surface of the battery cell through the reduced width portion. Positive electrode empty foil area 1-2 and negative electrode empty foil area 2-2 are respectively formed on both sides of the gap area 3-4. The outer shell 4 of the present invention has shell areas made of different materials, including a first metal shell area 4-1, an insulation connection area 4-2, and a second metal shell area 4-3 arranged in sequence. The positive electrode empty foil area 1-2 and the negative electrode empty foil area 2-2 on the battery cell 3 all fall into the first metal shell area 4-1 and the second metal shell area 4-3 respectively, and the insulation connection area 4-2 falls into the gap area 3-4 of the battery cell 3.

[0025] like Figure 2 As shown, the positive electrode includes a positive electrode loading region 1-1 and a positive electrode empty foil region 1-2. The metal foil in the positive electrode loading region 1-1 is coated with a positive electrode active material. The positive electrode empty foil region 1-2 is the portion of the metal foil without a positive electrode active material coating, such as aluminum foil. The positive electrode empty foil region 1-2 has a smaller width than the positive electrode loading region 1-1. Similarly, as... Figure 3 The negative electrode includes a negative electrode load region 2-1 and a negative electrode empty foil region 2-2. The metal foil in the negative electrode load region 2-1 is coated with a negative electrode active material. The empty foil region 2-2 is the portion of the metal foil without the negative electrode active material, such as copper foil. The empty foil region 2-2 has a smaller width than the negative electrode load region 2-1. The cell structure 3 formed after the positive and negative electrode sheets are wound together is as follows: Figure 4 As shown, positive electrode empty foil region 1-2, gap region 3-4, and negative electrode empty foil region 2-2 are sequentially formed on the surface. The outer casing 4 of this invention is as follows... Figure 5 As shown, the sequentially arranged first metal casing area 4-1, insulating connection area 4-2, and second metal casing area 4-3 correspond sequentially to the positive electrode empty foil area 1-2, gap area 3-4, and negative electrode empty foil area 2-2 of the battery cell 3, respectively. This allows the leads of the battery's positive and negative electrodes to be transferred to the outer casing through the empty foil areas, and then led out of the outer casing, thus replacing the lead-in function of the tabs. The correspondence between the intermediate gap area 3-4 and the insulating connection area 4-2 serves to isolate the positive and negative electrodes, preventing short circuits. Figure 7 As shown, this connection method can not only reduce the setting of the upper tab of the battery cell, but also simplify the design of the upper tab connector 5-5 of the cover plate 5, thereby reducing the space 6-1 design of this part.

[0026] To complete the receiving function, the outer shell 4 can be made of suitable metal materials for the first metal shell area 4-1 and the second metal shell area 4-3 respectively. Considering the hardness and conductivity requirements of the shell, the first metal shell area 4-1 can be made of aluminum (aluminum shell), the second metal shell area 4-3 can be made of steel (steel shell), and the insulating connection area 4-2 can be made of materials such as PP, ABS, PBT, etc.

[0027] The cover plate 5 structure of the present invention can be as follows: Figure 6 As shown, it can be divided into three layers from top to bottom. A step is formed between the first cover plate 5-1 and the second cover plate 5-2, corresponding to the thickness of the outer shell 4. Both layers are made of aluminum, facilitating the use of laser welding or other methods to create a welded seal between the cover plate 5 and the outer shell 4. The third cover plate 5-3 is an insulating layer, made of an insulating and electrolyte-resistant material, such as fluororubber. An injection hole 5-4 can also be opened on the cover plate 5 for injecting electrolyte.

[0028] To prevent leakage of the positive and negative electrodes, the bottom of the battery cell 3 also needs to be insulated and protected. This includes wrapping the bottom of the battery cell 3 with electrolyte-resistant and insulating tape, and insulating and corrosion-resistant the inner bottom surface of the outer casing 4.

[0029] To further explore the optimization and reliability of battery performance after the removal of the tabs in the structure of this invention, we optimized the structural parameters of this invention through experiments.

[0030] Figure 6 In this design, after the battery cell 3 is placed in the outer casing 4, the height of the space 6-1 is defined as gap A (in mm). The ratio between the thickness of the battery cell 3 and the thickness of the inner cavity of the outer casing 4 is the fill ratio B (in %). The ratio of the width of the empty foil area 1-2 of the positive electrode sheet to the width of the empty foil area 2-2 of the negative electrode sheet is the foil width ratio C. The ratio of the sum of the widths of the empty foil areas 1-2 of the positive electrode sheet and the empty foil area 2-2 of the negative electrode sheet to the width of the negative electrode load area 2-1 is the foil occupancy ratio D. Using battery model 533450 as an example, a battery cell with this structure is manufactured using the materials of this invention. The standard battery height is 50 mm, width is 34 mm, and thickness is 5 mm. To increase the contact between the positive and negative electrode foil areas and the outer casing 4, a higher foil coverage ratio D is generally desired. Therefore, a foil coverage ratio D of not less than 0.9 is preferable. Simultaneously, in battery design, the width of the negative electrode load area generally needs to be slightly larger than the width of the positive electrode load area to avoid lithium deficiency and ensure that all lithium is embedded in the negative electrode. Therefore, in the calculation of the foil coverage ratio D, it is more appropriate to define the total width (denominator) as the negative electrode load area 2-1. In the experimental design of this batch of battery models, the foil coverage ratio D is (21.5mm + 21.5mm) / 46mm = 0.935. The battery parameter designs for different experiments are listed in Table 1, and the results of testing the batteries obtained in the experiments are also listed in Table 1.

[0031] The capacity test method reads the discharge capacity of 0.2C. The specific test conditions are as follows: (1) let stand for 5 minutes; (2) 0.5C C to 4.35V, CV to 0.05C; (3) let stand for 5 minutes; (4) 0.2C DC to 3.0V; (5) end.

[0032] The short circuit test method and specific test conditions are as follows: (1) Test voltage 220V, test internal resistance 10 megohms; (2) If the internal resistance is less than 10 megohms, it is determined to be a short circuit.

[0033] The 130℃ hot box test method and specific test conditions are as follows: (1) Place the battery in the forced-air oven and heat the battery at a rate of 5℃ / min. When the temperature of the oven reaches the range of 130℃±2℃, start timing and stop heating when the battery has been placed inside for 60 minutes; (2) When the oven temperature drops below 50 degrees, check the oven to confirm the condition of the battery; (3) As long as the battery does not catch fire or explode, we consider it to have passed the test.

[0034] Table 1

[0035]

[0036]

[0037] The above experiments show that after the tabs are removed, the performance of the battery structure of the present invention, such as capacity, structural changes, safety and temperature resistance, will be affected by the degree of filling between the cell 3 and the outer casing 4.

[0038] For batteries that normally use metal strips as tabs, as shown in the control group of Experiments 1-6, the gap between the cell and the cover plate must be set to more than 5mm to reduce the short-circuit rate of the cell manufacturing process to below 1.5%. However, using the battery design of this invention, the gap between the cell and the cover plate can be compressed to 1mm, which increases the energy density of the battery to a considerable level (9.4%), as shown in Experiment 8.

[0039] Experiment 7-18 demonstrates the impact of changes in gap A. As the value of A decreases, the battery's thermal safety decreases somewhat, but overall it is still superior to batteries designed using traditional methods. When the value of A is between 1.5 mm and 2.5 mm, the safety is basically controlled within the ideal range, while when it is greater than 2.5 mm, the battery's thermal safety hardly changes. Therefore, the range of gap A can be designed as 0.5-6 mm, preferably 1-6 mm, more preferably 1.5-6 mm, and most preferably 1.5-2.5 mm.

[0040] Experiments 19-31 show the effect of changes in the fill ratio B. When the fill ratio B is less than 88%, the battery capacity deviates significantly from the theoretical value, and the battery temperature rise is also abnormal. This is likely related to the high contact resistance between the electrode and the casing. When the B value is greater than 95%, the battery thickness exceeds the standard. Therefore, the fill ratio B value of this invention is preferably between 88% and 95%.

[0041] Experiments 32-40 show the effect of the foil width ratio C. The width ratio C of the foil left at the end of the positive and negative electrode sheets has a certain impact on temperature rise and thermal safety performance. The experiment shows that the effect is best when the C value is close to 1. When it reaches 0.11 or 9, the failure rate has reached more than 15%. For better battery safety performance, it is generally recommended to control the failure rate to within 10% and control the C value between 0.4 and 2.3, preferably 1 ± 0.5.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-energy-density and high-safety tabless lithium-ion battery, comprising a cell (3) placed inside a housing (4), the housing (4) having a cover plate (5) on top; the cell (3) is formed by winding positive and negative electrodes separated by a separator, the ends of the positive and negative electrodes being designed as empty foil areas with reduced width, and the empty foil areas of the positive and negative electrodes forming a gap area (3-4) with spacing on the surface of the cell after winding through the reduced width portion, and positive electrodes being formed on both sides of the gap area (3-4). Empty foil area (1-2) and negative electrode empty foil area (2-2); the outer shell (4) has shell areas made of different materials, including a first metal shell area (4-1), an insulation connection area (4-2), and a second metal shell area (4-3) arranged in sequence. The positive electrode empty foil area (1-2) and the negative electrode empty foil area (2-2) on the cell (3) all fall into the first metal shell area (4-1) and the second metal shell area (4-3) respectively, and the insulation connection area (4-2) falls into the gap area (3-4) of the cell (3). The gap A between the top of the cell (3) and the bottom surface of the cover plate (5) inside the outer shell (4) is 1-6 mm; the ratio between the thickness of the cell (3) and the thickness of the inner cavity of the outer shell (4) is the filling ratio B, which is 88%-95%; the ratio between the width of the positive electrode empty foil area (1-2) and the width of the negative electrode empty foil area (2-2) is the foil width ratio C, with a specific value of 0.4-2.3; the ratio between the sum of the widths of the positive electrode empty foil area (1-2) and the negative electrode empty foil area (2-2) and the width of the negative electrode load area (2-1) is the foil occupancy ratio D, with a specific value of 0.9≤Foil Occupancy Ratio D<1.

2. The high energy density and high safety tabless lithium-ion battery according to claim 1, characterized in that, The first metal shell area (4-1) of the outer shell (4) is an aluminum shell, and the second metal shell area (4-3) is a steel shell.

3. The high energy density and high safety tabless lithium-ion battery according to claim 1, characterized in that, The cover plate (5) includes, from top to bottom, a first cover plate (5-1), a second cover plate (5-2) and a third cover plate (5-3). A step is formed between the first cover plate (5-1) and the second cover plate (5-2). The step corresponds to the shell thickness of the outer shell (4) and is made of aluminum. The third cover plate (5-3) is an insulating layer.

4. The high energy density and high safety tabless lithium-ion battery according to claim 1, characterized in that, The cover plate (5) has injection holes (5-4).

5. The high energy density and high safety tabless lithium-ion battery according to claim 1, characterized in that, The bottom of the battery cell (3) has an insulating protective layer.

6. The high energy density and high safety tabless lithium-ion battery according to claim 1, characterized in that, The gap A is 1.5-6mm.

7. The high energy density and high safety tabless lithium-ion battery according to claim 1, characterized in that, The gap A is 1.5-2.5mm.

8. The high energy density and high safety tabless lithium-ion battery according to claim 1, characterized in that, The foil width ratio C is 1 ± 0.5.

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