Negative plate and battery cell

Abstract

The utility model discloses a negative pole piece and a battery cell, which comprise a negative pole current collector and an active substance arranged on at least one functional surface of the negative pole current collector, and the negative pole current collector comprises a first area and a second area surrounding the periphery of the first area, the compaction density of the active substance on the second region is lower than that of the active substance on the first region, and the compaction density of the active substance in a tab side region adjacent to the tab on the second region is lower than that of the active substance in a non-tab side region. By optimizing the structure of the negative plate, the problem of lithium precipitation at the edge of the battery is solved, and the cycle performance and the safety performance of the battery are improved.

Description

Technical Field

[0001] This utility model relates to the field of lithium-ion battery technology, specifically to a negative electrode sheet and a battery cell. Background Technology

[0002] Typically, when designing battery cells, the size of the negative electrode needs to be larger than that of the positive electrode to take into account the differences in equipment manufacturing capabilities. Whether it is a stacked or wound design, the negative electrode will extend beyond the positive electrode at the edge after completely covering it. This extended area of ​​the negative electrode is called the Overhang area in the industry.

[0003] Currently, during the disassembly of cycled battery cells, it has been found that lithium plating in the overhang region of the negative electrode is more severe than in the body region, and the higher the charging rate, the more pronounced the lithium plating at the edges. Because the lithium-ion diffusion distance in the overhang region is longer than in the central area, the local impedance is greater, resulting in weaker kinetic performance at the electrode edges. The rate of lithium ion insertion and extraction between the positive and negative electrodes in the edge region is inconsistent with that in the central region, making lithium plating more likely at the edges of lithium-ion batteries. Lithium plating leads to further thickening of the negative electrode edges, causing further degradation of battery life or even battery performance failure. Furthermore, the presence of lithium dendrites generated by lithium plating can easily puncture the separator, causing a short circuit and potentially leading to a safety accident.

[0004] In particular, the lithium plating problem is more severe in the overhang region near the tabs compared to the non-tabs side. This is mainly because the current density at the tabs is higher, resulting in greater consumption of electrolyte. During charging and discharging, insufficient electrolyte is prone to occur at the tabs, leading to lithium plating and affecting the battery's cycle performance and safety performance.

[0005] Therefore, there is an urgent need for a new type of negative electrode and battery cell to improve the above problems. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this utility model is to provide a negative electrode sheet and a battery cell, which improves the lithium plating problem at the edge of the battery by optimizing the negative electrode sheet structure, thereby improving the cycle performance and safety performance of the battery.

[0007] To achieve the above objectives, this utility model is implemented through the following technical solution:

[0008] In a first aspect, the present invention provides a negative electrode sheet, comprising a negative electrode current collector and an active material disposed on at least one functional surface of the negative electrode current collector. The negative electrode current collector comprises a first region and a second region surrounding the first region. The compaction density of the active material in the second region is lower than that of the active material in the first region. The compaction density of the active material in the tab-side region of the second region adjacent to the tab is lower than that of the active material in the non-tab-side region.

[0009] As a further optimization of this utility model, the compaction density of the active material in the second region is 3%-10% lower than that of the active material in the first region.

[0010] As a further optimization of this utility model, the compaction density of the active material in the tab side region is 1%-3% lower than that of the active material in the non-tab side region.

[0011] As a further optimization of this utility model, the thickness of the second region is increased by 0-15 μm compared to the thickness of the first region.

[0012] As a further optimization of this utility model, the thickness of the tab side region is increased by 0-5 μm compared with the thickness of the non-tab side region.

[0013] As a further optimization of this utility model, the second region is rectangular in shape, and the width of the electrode side region is equal to the width of the non-electrode side region.

[0014] As a further optimization of this utility model, the width of the second region is greater than the width of the Overhang region.

[0015] As a further optimization of this utility model, the compaction density of the active material in the second region gradually decreases from the middle to the edge, and the thickness of the second region gradually increases from the middle to the edge.

[0016] As a further optimization of this utility model, the width of the second region is 1.5-2 times the width of the Overhang region.

[0017] Secondly, this utility model provides a battery cell, including a positive electrode, a separator, and a negative electrode, wherein the positive electrode, the separator, and the negative electrode are stacked.

[0018] Compared with the prior art, this utility model has the following advantages and beneficial effects:

[0019] This invention employs a zoned design for the negative electrode, reducing the compaction density of the second region (edge ​​region) and making its porosity higher than that of the first region (central large surface area). This allows the edge region to absorb more electrolyte, accelerating lithium-ion transport during charging and discharging. As described in the background art, the overhang region of the existing negative electrode exhibits weak kinetic performance due to its long lithium-ion diffusion distance and high local impedance. This design effectively solves this problem, improving the kinetic performance of the electrode edge.

[0020] This invention, on the one hand, reduces the edge compaction density, increases the porosity of the edge region, facilitates full electrolyte wetting, improves lithium ion transport conditions in the edge region, and reduces the possibility of lithium plating; on the other hand, it further divides the second region into a tab-side region and a non-tab-side region, reducing the compaction density of the tab-side region to form a high-porosity region. Although the current density and electrolyte consumption are high at the tab, the high-porosity region can better replenish the electrolyte, thereby effectively suppressing lithium plating in the tab-side overhang region. From the results of the embodiments, Embodiments 1 and 2, by reasonably controlling the edge compaction density, significantly improved the edge lithium plating situation after cyclic testing; Embodiment 2 even achieved zero edge lithium plating.

[0021] In this invention, the thickness of the second region is increased by 0-15 μm compared to the first region, and the thickness of the tab-side region is increased by 0-5 μm compared to the non-tab-side region. This thickness variation allows the positive and negative electrodes to adhere more tightly during stacking. Tight adhesion reduces edge impedance, minimizing energy loss and lithium plating risk caused by impedance, thus further ensuring battery performance and cycle life. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the negative electrode sheet of this utility model.

[0023] Figure 2 This is a schematic diagram of the stacked structure of the battery cell of this utility model.

[0024] Explanation of reference numerals in the attached diagram: 1-Negative electrode; 11-Negative current collector; 101-First region; 102-Second region; 103-Overhang region; 1001-Taper side region; 1002-Non-Taper side region; 2-Separator; 3-Positive electrode; 4-Taper. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solution of this utility model, the preferred embodiments of this utility model are described below in conjunction with specific examples. However, it should be understood that the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable for those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0026] Please see Figure 1This invention provides a negative electrode sheet 1, which includes a negative electrode current collector 11 and active materials disposed on the front and back surfaces of the negative electrode current collector 11. The negative electrode current collector 11 includes a first region 101 and a second region 102 surrounding the first region 101. The compaction density of the active material in the second region 102 is lower than that in the first region 101. The compaction density of the active material in the tab-side region 1001 of the second region 102, which is immediately adjacent to the tab 4, is lower than that in the non-tab-side region 1002. The areal density of the first region 101 and the second region 102 is the same.

[0027] As can be seen from the above structural design, the negative electrode 1 is partitioned. By reducing the compaction density of the edge region (second region 102), the porosity of the edge region is made higher than that of the central large surface region (first region 101), which can adsorb more electrolyte, resulting in faster lithium-ion transport during charging and discharging and reducing the risk of lithium deposition in the edge overhang region. At the same time, the edge region (second region 102) of the negative electrode 1 is divided into two regions: the tab side region 1001 and the non-tab side region 1002. The compaction density of the tab side region 1001 is set to be lower in order to form a high porosity region, thereby further reducing the risk of lithium deposition in the overhang region on the tab side.

[0028] In the process of optimizing the edge structure of the negative electrode sheet 1, this utility model maintains the compaction density of the large central area unchanged, which makes the overall energy density of the battery almost unaffected. While improving other battery performance, it ensures the energy storage capacity of the battery and meets the actual use needs.

[0029] In some optional embodiments, the compaction density of the active material in the second region 102 is 3%-10% lower than that of the active material in the first region 101. This density difference ensures that the first region 101 has a higher compaction density to maintain the battery's energy density, while also allowing the second region 102 to form higher porosity, enhancing the electrolyte's adsorption capacity and improving the kinetic performance of the edge region. The compaction density of the active material in the tab-side region 1001 of the second region 102, immediately adjacent to the tab 4, is 1%-3% lower than that of the active material in the non-tab-side region 1002. The lower compaction density of the tab-side region 1001 can form a high-porosity region, better replenishing the electrolyte consumed due to the high current density at the tab 4, and reducing the risk of lithium plating in the overhang region on the tab 4 side.

[0030] In some optional embodiments, the thickness of the second region 102 is increased by 0-15 μm compared to the thickness of the first region 101. This increased electrode edge thickness allows the positive and negative electrodes to fit more tightly during stacking, thereby reducing edge impedance and further minimizing the risk of lithium plating at the electrode edges. The thickness of the tab-side region 1001 on the second region 102, immediately adjacent to the tab 4, is increased by 0-5 μm compared to the thickness of the non-tab-side region 1002. This fine-tuning of the tab-side region thickness helps to further optimize the structure of the area near the tab, ensuring good performance at the tab.

[0031] In some alternative embodiments, the second region 102 is rectangular in shape, and the width of the tabular side region 1001 is equal to the width of the non-tabular side region 1002.

[0032] As can be seen from the above structural design, the rectangular second region 102 is simple to design and easy to manufacture, ensuring product consistency and stability during mass production. The tab-side region 1001 and the non-tab-side region 1002 have equal widths, resulting in a symmetrical design across the entire edge area. This facilitates a uniform current distribution along the electrode edge during charging and discharging, preventing localized excessive or insufficient current due to regional differences, further reducing the possibility of lithium plating and improving battery safety and reliability. Simultaneously, this symmetrical design also facilitates quality inspection and control during production, reducing errors and scrap rates.

[0033] In some optional embodiments, the width of the second region 102 is greater than the width of the overhang region, and the width of the second region 102 is 1.5-2 times the width of the overhang region. The compaction density of the active material on the second region 102 gradually decreases from the center to the edge, and the thickness of the second region 102 gradually increases from the center to the edge.

[0034] As can be seen from the above structural design, the width of the second region 102 is greater than that of the Overhang region and falls within a specific proportional range, enabling more comprehensive optimization of the easily lithium-plated Overhang region and its surroundings. The compaction density gradually decreases from the center to the edge, further expanding the high porosity range of the edge region. This allows for better electrolyte adsorption throughout the edge area, facilitating smoother lithium-ion transport and significantly reducing the risk of lithium plating from the Overhang region to the wider edge region. The thickness gradually increases from the center to the edge, ensuring tight adhesion between the positive and negative electrode sheets 1 from the center to the edge. This also alleviates stress concentration caused by poor lithium-ion transport in the edge region to some extent, further reducing impedance and improving the overall performance and stability of the battery.

[0035] A battery cell includes a positive electrode 3, a separator 2, and a negative electrode 1, wherein the positive electrode 3, the separator 2, and the negative electrode 1 are stacked together. Figure 2 As shown. Specifically, the multilayer electrode sheets and separator 2 are stacked layer by layer in the arrangement of separator 2-negative electrode sheet 1-separator 2-positive electrode sheet 3. The n-layer positive electrode sheet 3 and the n+1-layer negative electrode sheet 1 are connected to the positive electrode tab 4 and the negative electrode tab 4 respectively by welding.

[0036] The battery cells are assembled into a lithium-ion battery. The performance testing methods for lithium-ion batteries are as follows:

[0037] Capacity retention rate after 1000 cycles: Charge the battery at a constant current and constant voltage of 1C to 3.65V, cut off the current at 0.05C, and let it rest for 30 minutes; then discharge it at a 1C current to the discharge termination voltage of 2.5V, and let it rest for 30 minutes; repeat the above two steps for a total of 1000 times, record the first discharge capacity as the battery discharge capacity C1, and the discharge capacity of the 1000th cycle as C1000; 1000-cycle capacity retention rate % = (C1000 / C1) × 100%.

[0038] The ACR growth rate after 1000 cycles: Charge the battery at a constant current and voltage of 1C to 3.65V, cut off the current at 0.05C, and let it rest for 30 minutes; then discharge it at a 1C current for 30 minutes, and let it rest for 30 minutes; test the battery's initial ACR, and record it as ACR1; charge the battery at a constant current and voltage of 1C to 3.65V, cut off the current at 0.05C, and let it rest for 30 minutes; then discharge it at a 1C current to the discharge termination voltage of 2.5V, and let it rest for 30 minutes; repeat the above two steps for a total of 1000 times. After the cycle is completed, charge the battery at a constant current and voltage of 1C to 3.65V, cut off the current at 0.05C, and let it rest for 30 minutes; then discharge it at a 1C current for 30 minutes, and let it rest for 30 minutes; test the battery's initial ACR, and record it as ACR2. The ACR growth rate % after 1000 cycles = (ACR2 - ACR1) / ACR1 × 100%.

[0039] Disassembly after 500 cycles: The battery was charged at a constant current and constant voltage of 1C to 3.65V, with a cutoff current of 0.05C, and left to rest for 30 minutes; then discharged at a 1C current to the discharge termination voltage of 2.5V, and left to rest for 30 minutes; the above two steps were repeated for a total of 500 times; after the cycle test was completed, the battery was charged at a constant current and constant voltage of 1C to 3.65V, with a cutoff current of 0.05C, and the battery was disassembled after being fully charged.

[0040] The performance test results of the lithium-ion battery are shown in Table 1 below.

[0041] Table 1

[0042]

[0043] Table 1 shows that the areal density is 200 g / m³. 2 The compaction density of the large surface area is 1.65 g / m³. 3 The only difference was the edge compaction density. As the edge compaction density increased, the capacity retention after 1000 cycles decreased, the ACR growth rate after 1000 cycles increased, and edge lithium plating worsened during disassembly after 500 cycles. For example, in Example 1, the edge compaction density was 1.50 g / m³. 3 Capacity retention was 90.5%, ACR growth rate was 40.0%, and slight lithium plating was observed at the edges; the edge compaction density in Example 4 was 1.65 g / m³. 3 The capacity retention rate was 86.4%, the ACR growth rate was 50.3%, and significant lithium plating was observed at the edges. This indicates that reducing the edge compaction density can suppress lithium plating and improve battery cycle performance, verifying the design concept of this invention to improve battery performance by changing the edge compaction density of the negative electrode. However, excessively reducing the edge compaction density can also lead to lithium plating problems, so the edge compaction density needs to be controlled within a reasonable range.

[0044] The disassembly results after 500 cycles in Examples 1-4 corroborate the data in Table 1. Example 1 showed slight lithium plating at the edges, Example 2 showed no lithium plating at the edges, and Examples 3 and 4 showed significant lithium plating at the edges. This clearly and intuitively presents the lithium plating situation of the battery under different edge compaction densities, demonstrating from a practical disassembly perspective the effect of reducing edge compaction density on suppressing lithium plating, making the research results more convincing.

[0045] Table 1 shows that the design of reducing the edge compaction density of the negative electrode sheet in this invention can effectively suppress lithium plating at the battery edge and improve battery cycle performance. The design in Example 2 shows the best performance in suppressing lithium plating and improving cycle performance, providing valuable reference for negative electrode sheet and cell design. These two designs complement each other, providing strong support for a deeper understanding of battery performance variation patterns and optimizing battery design, thus promoting the development of lithium-ion battery technology.

[0046] Based on the description and drawings of this utility model, those skilled in the art can easily manufacture or use a negative electrode sheet and a battery cell of this utility model, and can produce the positive effects described in this utility model.

[0047] Unless otherwise specified, in this utility model, terms such as "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this utility model 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, the terms used to describe orientation or positional relationships in this utility model are for illustrative purposes only and should not be construed as limiting this patent. For those skilled in the art, the specific meaning of the above terms can be understood in conjunction with the accompanying drawings and according to the specific circumstances.

[0048] Unless otherwise expressly specified and limited, the terms "set up," "connected," and "linked" in this utility model should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0049] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present utility model shall fall within the protection scope of the present utility model.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector (11) and an active material disposed on at least one functional surface of the negative electrode current collector (11), characterized in that: The negative electrode current collector (11) includes a first region (101) and a second region (102) surrounding the first region (101). The compaction density of the active material in the second region (102) is lower than that of the active material in the first region (101). The compaction density of the active material in the tab side region (1001) of the second region (102) adjacent to the tab (4) is lower than that of the active material in the non-tab side region (1002).

2. The negative electrode sheet according to claim 1, characterized in that: The compaction density of the active material in the second region (102) is 3%-10% lower than that of the active material in the first region (101).

3. The negative electrode sheet according to claim 1, characterized in that: The compaction density of the active material in the tabular region (1001) is 1%-3% lower than that of the active material in the non-tabular region (1002).

4. The negative electrode sheet according to claim 1, characterized in that: The thickness of the second region (102) is increased by 0-15 μm compared to the thickness of the first region (101).

5. The negative electrode sheet according to claim 1, characterized in that: The thickness of the polar ear side region (1001) is increased by 0-5 μm compared to the thickness of the non-polar ear side region (1002).

6. The negative electrode sheet according to claim 1, characterized in that: The second region (102) is rectangular in shape, and the width of the polar ear side region (1001) is equal to the width of the non-polar ear side region (1002).

7. The negative electrode sheet according to claim 1, characterized in that: The width of the second region (102) is greater than the width of the Overhang region (103).

8. The negative electrode sheet according to claim 7, characterized in that: The compaction density of the active material in the second region (102) gradually decreases from the center to the edge, and the thickness of the second region (102) gradually increases from the center to the edge.

9. The negative electrode sheet according to claim 7, characterized in that: The width of the second region (102) is 1.5 to 2 times the width of the Overhang region (103).

10. A battery cell, characterized in that: It includes a positive electrode (3), a separator (2) and a negative electrode (1) as described in any one of claims 1 to 9, wherein the positive electrode (3), the separator (2) and the negative electrode (1) are stacked.

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