Electrodes for improving lithium plating at corners, their preparation methods, and battery cells

Abstract

This invention relates to the technical field of battery manufacturing, specifically to a negative electrode sheet for improving lithium plating at corners, its preparation method, and a battery cell. The negative electrode sheet includes a substrate, which includes at least one first corner region and at least one first non-corner region, with the first corner region and the first non-corner region alternating. At least one side surface of the first corner region is provided with a plurality of uniformly spaced current-guiding protrusions arrayed, each current-guiding protrusion array comprising a plurality of protrusions arranged in an array. This invention, through the design of the current-guiding protrusion array, increases the local conductive contact area, disperses the current density at the corner, suppresses local current density concentration in the corner region, and avoids lithium plating in the corner region of the lithium-ion battery under fast charging or low-temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and more specifically to a negative electrode sheet for improving lithium plating at corners, a method for preparing the same, and a battery cell. Background Technology

[0002] Wound-type battery cells are prone to lithium plating during cycling. Especially at the corners of the electrodes, the space constraints lead to uneven current density distribution, making the corner areas high-risk regions for lithium plating. This further increases the risk of capacity decay, increased internal resistance, and even thermal runaway in battery cells using this type of electrode.

[0003] To address the aforementioned issues, some existing technologies have reported improvements in lithium plating at the corners of the electrode by employing special designs.

[0004] For example, invention patent application CN202411642688.3 discloses a wound battery. The wound battery includes a negative electrode, a positive electrode, and a separator. In the corner area of ​​the wound battery, the negative electrode has a recessed portion facing the inner material area inside the battery. The recessed portion has the same depth at all locations. Except for the recessed portion, the thickness of the inner material area is consistent in the corner area. Similarly, the thickness of the outer material area facing outwards from the negative electrode is consistent in the corner area, and the inner and outer material areas are of equal thickness. This wound battery reduces lithium plating in the corner area by designing multiple recessed portions at the corners of the electrode, thus improving the electrolyte wetting process.

[0005] For example, patent application CN202420963039.2 discloses an electrode and a battery cell assembly. The electrode includes a current collector, an active material layer, and an electrolyte expansion layer. The active material layer is coated on at least one side of the current collector. The active material layer and the current collector form the electrode. The active material layer is wound around the current collector. The electrode includes a corner region where a corner is formed during winding. The electrolyte expansion layer is disposed on the surface of the active material layer and is located in the corner region. By providing an electrolyte expansion layer in the corner region of the electrode, the gap between adjacent electrodes is sufficient to allow electrolyte flow, thereby preventing lithium plating in the corner region.

[0006] It is evident that a common approach to mitigating lithium plating at the corners of wound battery cells in existing technologies is to improve the electrolyte wettability in the corner region. However, this method, which relies on improving electrolyte wettability, still has some limitations: the actual wetting effect of the electrolyte is subject to various factors such as the electrolyte's own properties (viscosity, surface tension), the amount of electrolyte injected, and the injection process. As the electrolyte is consumed and deteriorates during cyclic aging, simply optimizing wettability is insufficient to completely suppress the high current density concentration at the corner due to space constraints. Therefore, it is urgent to explore electrode design schemes that can be directly used to optimize current distribution and improve local ion dynamics. Summary of the Invention

[0007] To address the aforementioned issues, this invention provides a negative electrode sheet for improving lithium plating at corners, its preparation method, and a battery cell. The negative electrode sheet, through the design of a current-guiding protrusion array, increases the local conductive contact area, disperses the current density at corners, suppresses the concentration of local current density in the corner region, and avoids lithium plating in the corner region of lithium-ion batteries under fast charging or low-temperature conditions.

[0008] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0009] In a first aspect, the present invention provides a negative electrode sheet for improving lithium plating at corners, comprising a substrate, the substrate comprising at least a first corner region and at least a first non-corner region, the first corner region and the first non-corner region being alternately distributed; at least one side surface of the first corner region is provided with a plurality of uniformly spaced current-guiding protrusion arrays, the current-guiding protrusion arrays comprising a plurality of protrusions arranged in an array.

[0010] The current-guiding protrusion array of the present invention can optimize the electron transport path by increasing the local conductive contact area, directly disperse the highly concentrated current density at the corner, and allow it to flow to a wider space through the protrusions arranged in the array. This reduces the driving force of lithium plating from the source, and this improvement is not limited by electrolyte consumption or deterioration, thus having a wider range of applications.

[0011] Preferably, the diameter of the protrusion is 10~50μm.

[0012] The diameter design of the protrusions should meet the need for increased local conductive area, while avoiding excessively large protrusions that could lead to decreased mechanical properties or increased manufacturing difficulty, thus negatively impacting conductivity. This diameter range can cover the microscopic uneven areas on the substrate surface, preventing lithium dendrites from piercing through, while also buffering stress impacts through the flexibility of the polymer substrate. It also avoids the risk of exposed protrusion arrays due to excessively thin electrode sheets, further optimizing local current distribution and preventing energy density loss due to increased weight.

[0013] Preferably, the distance between the two protrusions is 100~500μm.

[0014] Excessive spacing between the two protrusions can lead to uneven current distribution, while insufficient spacing increases process complexity and cost, and introduces the risk of uneven electrolyte wetting. This spacing range effectively disperses the concentrated current at the corner to the adjacent protrusion, alters the electric field distribution, suppresses the vertical growth of lithium dendrites and guides their lateral expansion, reducing the risk of puncturing the separator.

[0015] Preferably, the substrate includes one of copper foil and composite copper foil.

[0016] Preferably, the thickness of the substrate is 5~8 μm.

[0017] Preferably, the composite copper foil comprises a copper layer and a polymer layer, wherein the polymer layer comprises one of polyethylene terephthalate (PET), polypropylene (PP), and polyimide (PI).

[0018] Preferably, the thickness of the polymer layer is 3~6 μm.

[0019] Preferably, the thickness of the copper layer is 0.02~1 μm.

[0020] Preferably, the substrate further includes a coating layer formed by coating a conductive polymer on at least one side surface of the substrate. The coating layer includes at least one second corner region and at least one second non-corner region. The second corner region is disposed corresponding to the first corner region, and the second non-corner region is disposed corresponding to the first non-corner region. The porosity of the conductive polymer in the second corner region is greater than the porosity of the conductive polymer in the second non-corner region.

[0021] By designing a porosity gradient, the electrode has more and more unobstructed micropore channels in the corner region, thereby improving ion permeability. Furthermore, the improved lithium-ion transport capability synergizes with the optimized electron transport provided by the current-guiding protrusion array, effectively reducing polarization and further suppressing lithium plating.

[0022] Preferably, the conductive polymer comprises poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS).

[0023] Preferably, the porosity of the conductive polymer in the second corner region is 0% to 25% higher than that of the conductive polymer in the second non-corner region.

[0024] Preferably, the coating further includes an active material layer formed by coating an active material on the surface of the coating layer away from the substrate. The active material includes an adhesive. The active material layer includes at least one third corner region and at least one third non-corner region. The third corner region is corresponding to the first corner region, and the third non-corner region is corresponding to the first non-corner region. The adhesive content in the third corner region is greater than the adhesive content in the third non-corner region.

[0025] By designing a gradient in binder content, the mechanical strength of the electrode in the corner area can be increased, ensuring that the current-guiding protrusion array and pore gradient design can effectively optimize current distribution and ion transport over a long period of time. This means that the design can be stably maintained under long-term charge-discharge cycles, volume changes, and mechanical stress, preventing structural failure from causing new lithium plating risks.

[0026] Preferably, the active material includes one of natural graphite, artificial graphite, and hard carbon.

[0027] Preferably, the binder comprises sodium carboxymethyl cellulose (CMC).

[0028] Preferably, the adhesive content in the third corner area is 5% to 10% higher than the adhesive content in the third non-corner area.

[0029] Secondly, the present invention also provides a method for preparing a negative electrode sheet to improve lithium plating at corners, comprising the following steps:

[0030] S1. A plurality of uniformly spaced flow-guiding protrusions are arranged on the first corner area of ​​the substrate;

[0031] S2. A conductive polymer is coated on at least one surface of the substrate to form a coating layer;

[0032] S3. The active material is coated onto the surface of the coating layer away from the substrate to form an active material layer. The coating is then dried, rolled, and cut to obtain a negative electrode sheet for improving lithium plating at corners.

[0033] Preferably, in step S1, the flow-guiding protrusion array is prepared by photolithography etching or 3D printing.

[0034] Thirdly, the present invention also provides a battery cell comprising a negative electrode sheet, a positive electrode sheet, and a separator as described above for improving lithium plating at corners, wherein the negative electrode sheet, the positive electrode sheet, and the separator are stacked and wound in the same direction to form the battery cell.

[0035] The beneficial effects of this invention are as follows:

[0036] 1. This invention increases the local conductive contact area of ​​the electrode by designing a current-guiding protrusion array, disperses the current density at the corner, and suppresses the concentration of local current density in the corner area, thereby effectively avoiding lithium plating in the corner area of ​​the electrode.

[0037] 2. This invention, through a gradient design of porosity, optimizes the electron transport path and further increases the ion transport capacity in the corner region, thereby further reducing lithium plating.

[0038] 3. This invention enhances the mechanical stability of the corner region through the gradient design of the binder, and can effectively maintain the effectiveness of the flow-guiding protrusion array and pore gradient design in optimizing the electrochemical environment under long-term cycling and harsh conditions. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the negative electrode structure;

[0040] Figure 2 This is a schematic diagram of the substrate for the negative electrode sheet;

[0041] Figure 3 This is a schematic diagram of the battery cell structure;

[0042] Figure 4 This is a partially enlarged schematic diagram of the battery cell.

[0043] In the picture:

[0044] 100, Negative electrode sheet; 110, Substrate; 111, First corner region; 112, First non-corner region; 113, Current-guiding protrusion array; 114, Protrusion; 120, Coating layer; 121, Second corner region; 122, Second non-corner region; 130, Active material layer; 131, Third corner region; 132, Third non-corner region; 200, Separator; 300, Positive electrode sheet. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0046] Example 1

[0047] S1. Dimensional analysis was performed according to the selected wound cell model (100Ah lithium iron phosphate wound cell). The dimensions of the electrode after winding are: length 8943±3 mm, width 100±0.5 mm, and thickness 188±2 μm. The wound cell after liquid injection and aging was laid out to determine the total length of the electrode, the length of each corner area on the electrode, and the length of each non-corner area. The corner areas and non-corner areas on the electrode were alternately set.

[0048] Composite copper foil is selected as the substrate 110. The substrate 110 includes a first corner area 111 corresponding to the corner area and a first non-corner area 112 corresponding to the non-corner area. The composite copper foil has a copper layer and a polymer layer. The polymer layer is made of PET with a thickness of 4 μm and the copper layer has a thickness of 1 μm. According to the test dimensions, a flow guiding protrusion array 113 is formed on the first corner area 111 of the substrate 110 by photolithography etching. The flow guiding protrusion array 113 includes a plurality of protrusions 114 arranged in an array. The diameter of the protrusions 114 is 30 μm and the spacing between two protrusions 114 is 300 μm.

[0049] S2. A conductive polymer PEDOT:PSS is coated on both sides of the substrate 110 to form a coating layer 120. The coating layer 120 includes a second corner region 121 corresponding to the corner region and a second non-corner region 122 corresponding to the non-corner region. The porosity of the second non-corner region 122 is 5%, and the porosity of the second corner region 121 is 15%.

[0050] S3. The negative electrode active material is coated onto the surface of the coating layer 120 away from the substrate 110 to form an active material layer 130, and then dried, rolled and cut to obtain a negative electrode sheet 100. The negative electrode active material includes graphite and a binder, the binder is CMC, and its content in the third corner region 131 is 8.8%, and its content in the third non-corner region 132 is 1.3%.

[0051] Cell manufacturing

[0052] The prepared negative electrode 100 is wound together with the positive electrode 300 and the separator 200 to form a bare battery cell. The material and size of the positive electrode 300 and the separator 200 can be the same as the selected winding battery cell model; the positive electrode active material used in the positive electrode 300 is lithium iron phosphate, and the positive electrode current collector is aluminum foil.

[0053] Example 2

[0054] It is basically the same as Example 1, except that the diameter of the protrusion 114 is 10 μm and the distance between the two protrusions 114 is 500 μm.

[0055] Example 3

[0056] It is basically the same as Example 1, except that the diameter of the protrusion 114 is 50 μm and the distance between the two protrusions 114 is 100 μm.

[0057] Example 4

[0058] The results are basically the same as in Example 1, except that the porosity of the conductive polymer in the second non-corner region 122 is 5%, and the porosity in the second corner region 121 is 5%.

[0059] Example 5

[0060] The results are basically the same as in Example 1, except that the porosity of the conductive polymer in the second non-corner region 122 is 5%, and the porosity in the second corner region 121 is 30%.

[0061] Example 6

[0062] It is basically the same as Example 1, except that the content of adhesive in the third corner region 131 is 6.3% and the content in the third non-corner region 132 is 1.3%;

[0063] Example 7

[0064] It is basically the same as Example 1, except that the content of adhesive in the third corner region 131 is 11.3% and the content in the third non-corner region 132 is 1.3%;

[0065] Comparative Example 1

[0066] The method is basically the same as in Example 1, except that: no flow-guiding protrusion array 113 is provided on the substrate 110, there is no coating layer 120, and the content of adhesive in different areas remains unchanged at 1.3%;

[0067] Comparative Example 2

[0068] It is basically the same as Example 1, except that the diameter of the protrusion 114 is 5μm and the distance between the two protrusions 114 is 600μm.

[0069] Comparative Example 3

[0070] It is basically the same as in Example 1, except that the diameter of the protrusion 114 is 70 μm and the distance between the two protrusions 114 is 80 μm.

[0071] Comparative Example 4

[0072] The results are basically the same as in Example 1, except that the porosity of the conductive polymer in the second non-corner region 122 is 5%, and the porosity in the second corner region 121 is 40%.

[0073] Comparative Example 5

[0074] It is basically the same as Example 1, except that the content of adhesive in the third corner region 131 is 15% and the content in the third non-corner region 132 is 1.3%.

[0075] Performance testing

[0076] After cycling the cells prepared in the above embodiments and comparative examples for 500 cycles, the batteries were disassembled under the following conditions: 1C, room temperature, and finally, the cells were disassembled in a dry room (dew point temperature ≤ -45℃) while fully charged. The results are shown in Table 1 below.

[0077] Table 1 Comparison of test results between Examples 1-7 and Comparative Examples 1-5

[0078] Group Battery disassembly <![CDATA[Single diversion area (μm 2 )]]> <![CDATA[Flow area increase (mm 2 )]]> Weight reduction (g) Example 1 No lithium plating in the corner area 706.858 316.756 62.885 Example 2 No lithium plating in the corner area 78.540 14.736 62.995 Example 3 No lithium plating in the corner area 1963.495 4258.603 61.448 Example 4 No lithium plating in the corner area 706.858 316.756 60.725 Example 5 No lithium plating in the corner area 706.858 316.756 69.365 Example 6 There was no lithium plating in the corner area, but there was slight powder shedding. 706.858 316.756 62.285 Example 7 No lithium plating in the corner area 706.858 316.756 61.485 Comparative Example 1 Lithium plating in the corner area 0 0 0 Comparative Example 2 Slight lithium plating was observed in the corner area. 19.635 2.618 62.999 Comparative Example 3 A raised array is exposed in the corner area. 3848.451 8346.863 62.692 Comparative Example 4 Slight lithium plating was observed in the corner area. 706.858 316.756 57.485 Comparative Example 5 The electrode in the corner area has cracks, and there is slight lithium plating at the cracks. 706.858 316.756 61.685

[0079] As shown in Table 1 above, Examples 1-7 illustrate that with a suitable size of the current-guiding protrusion array design, a suitable porosity gradient design, and a suitable binder gradient design, no lithium plating occurred in the electrode corner area after cell disassembly following 500 cycles. In Comparative Example 2, lithium plating occurred in the electrode corner area after disassembly, indicating that the individual current-guiding and total current-guiding areas were too small to achieve the desired effect. In Comparative Example 3, the protrusion array was exposed in the corner area after disassembly, indicating that the current-guiding array size was too large, resulting in an insufficient active material layer thickness and a risk of current collector leakage. In Comparative Example 4, slight lithium plating was observed in the electrode corner area after disassembly, indicating that excessively high porosity of the conductive polymer increased electron transport resistance, increasing the risk of lithium plating. In Comparative Example 5, cracks were found in the electrode corner area after disassembly, with slight lithium plating at the cracks, indicating that excessively high binder content reduced electrode flexibility, leading to electrode cracking and lithium plating risks.

Claims

1. A negative electrode sheet for improving lithium precipitation at a corner, characterized by The substrate (110) includes at least one first corner region (111) and at least one first non-corner region (112), which are alternately distributed. At least one side surface of the first corner region (111) is provided with a plurality of uniformly spaced flow-guiding protrusion arrays (113), each array of flow-guiding protrusion arrays (113) including a plurality of arrayed protrusions (114). The substrate (110) also includes a coating layer (120) formed by coating a conductive polymer onto at least one side surface of the substrate (110). The coating layer (120) includes at least one second corner region (121) and at least one second non-corner region (122), the second corner region (121) corresponding to the first corner region (111), and the second non-corner region (122)... 2) Corresponding to the first non-corner region (112); the porosity of the conductive polymer on the second corner region (121) is greater than the porosity of the conductive polymer on the second non-corner region (122); it also includes an active material layer (130) formed by coating an active material on the surface of the coating layer (120) away from the substrate (110), the active material including an adhesive, the active material layer (130) including at least one third corner region (131) and at least one third non-corner region (132), the third corner region (131) corresponding to the first corner region (111), the third non-corner region (132) corresponding to the first non-corner region (112); the content of adhesive on the third corner region (131) is greater than the content of adhesive on the third non-corner region (132).

2. The negative electrode sheet for improving lithium precipitation at a corner according to claim 1, characterized by, The diameter of the protrusion (114) is 10~50μm.

3. The negative electrode sheet for improving lithium precipitation at a corner according to claim 1, characterized by, The distance between two adjacent protrusions (114) is 100~500μm.

4. The negative electrode sheet for improving lithium precipitation at a corner according to claim 1, characterized by, The porosity of the conductive polymer in the second corner region (121) is 5% to 25% higher than that of the conductive polymer in the second non-corner region (122).

5. The negative electrode sheet for improving lithium precipitation at a corner according to claim 1, characterized by, The adhesive content in the third corner region (131) is 5% to 10% higher than the adhesive content in the third non-corner region (132).

6. A method for producing the negative electrode sheet for improving lithium precipitation at a corner according to any one of claims 1 to 5, characterized by, Includes the following steps: S1. A plurality of uniformly spaced flow-guiding protrusions array (113) are provided on the first corner area (111) of the substrate (110). S2. A conductive polymer is coated on at least one side surface of the substrate (110) to form a coating layer (120). S3. The active material is coated onto the surface of the coating layer (120) away from the substrate (110) to form an active material layer (130), and then dried, rolled and cut to obtain a negative electrode sheet (100) for improving lithium plating at the corner.

7. The method for preparing a negative electrode sheet for improving lithium plating at corners according to claim 6, characterized in that, In step S1, the flow-guiding protrusion array (113) is prepared by photolithography etching or 3D printing.

8. A battery cell, characterized in that, The negative electrode sheet (100) for improving lithium precipitation at a corner according to any one of claims 1 to 5, a positive electrode sheet (300), and a separator (200) are stacked and wound in the same direction to form the battery cell.

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