Anti-wrinkle winding type positive electrode sheet, preparation method thereof and winding core

Abstract

The application discloses a wrinkle-proof winding positive pole piece, a preparation method thereof and a winding core. The positive pole piece is not only covered with positive material layers with different thicknesses on a positive current collector, but also has recessed embossings with different depths in different regions, so that the loss of energy density caused by the fact that part of the positive current collector is not coated with the positive material layer due to interval coating can be avoided, the thickness of the pole piece at a winding position of the positive pole piece is smaller than the thickness of the pole piece at other positions after winding, the gap at the winding position is larger than the gap of a main surface after winding is completed, and after the pole piece is heated and expanded, the excess stress release space can be provided at the winding position, the uniformity of the internal stress of the winding core is ensured, the winding core deformation and the pole piece wrinkle phenomenon can be better reduced, meanwhile, the absorption and dispersion stress effect of the positive pole piece at the winding position can be obviously increased, the anti-wrinkle and cycle performance of the electrode pole piece is obviously improved, and the large-scale application of the winding positive pole piece is facilitated.

Description

Technical Field

[0001] This invention relates to the field of battery electrode technology, and in particular to an anti-wrinkle wound positive electrode, its preparation method, and the core thereof. Background Technology

[0002] With continuous breakthroughs in material technology and manufacturing processes for secondary batteries such as lithium-ion batteries, secondary batteries have been widely used in various fields, bringing convenience to people's production and daily life. However, during the large-scale production and application of secondary batteries, it has been discovered that existing cores suffer from uneven stress distribution during production and use, leading to wrinkles on the positive electrode sheet. This severely affects the electrical performance and lifespan of the core. As a crucial component of secondary batteries, the core directly impacts the battery's electrical performance and lifespan, thus limiting the large-scale promotion and application of secondary batteries. Summary of the Invention

[0003] The purpose of this invention is to address the problem of reduced electrical performance and lifespan caused by wrinkling in existing positive electrode sheets. This invention proposes a wrinkle-resistant wound positive electrode sheet, its preparation method, and the core. By specifically designing the partitioning and thickness of the positive electrode material layer and limiting the embossing depth in different areas, this invention avoids energy density loss caused by the lack of coating on the upper part of the positive current collector due to intermittent coating, effectively improving the energy density and cycle life of the positive electrode sheet. Furthermore, it provides extra stress release space at the winding point, significantly increasing the absorption and dispersion of stress at the winding point, ensuring the uniformity of internal stress in the battery cell, reducing core deformation and electrode wrinkling, and significantly improving the anti-wrinkle and cycle performance of the electrode sheet. This is beneficial for the large-scale application of wound positive electrode sheets.

[0004] To achieve the above objectives, the present invention provides a wrinkle-resistant wound positive electrode sheet, comprising a positive current collector and a positive electrode material layer covering the positive current collector; the positive electrode material layer is divided into a first coating area and a second coating area; the thickness of the second coating area is less than the thickness of the first coating area; the second coating area corresponds to the bend portion during the winding of the positive electrode sheet; the width of the first coating area and the second coating area gradually increases along the winding direction from the starting point of the positive electrode sheet winding; the positive electrode material layer is provided with recessed embossing, and the depth of the recessed embossing in the first coating area is 5-10% of the corresponding electrode sheet thickness, and the depth of the recessed embossing in the second coating area is 5-8% of the corresponding electrode sheet thickness.

[0005] This invention discloses a wrinkle-resistant wound positive electrode sheet. Not only is the positive electrode material layer coated on all positive current collectors, thus avoiding energy density loss caused by gaps in the coating and resulting in uncoated areas, the energy density and cycle life of the positive electrode sheet are effectively improved. Furthermore, the positive electrode material layers have varying thicknesses, ensuring that the thickness at the wound point is less than at other locations after winding. This results in a larger gap at the wound point compared to the main body surface, providing additional stress release space at the wound point after thermal expansion, ensuring uniform stress within the cell, and maintaining the flatness of the core and electrode sheet, further reducing core deformation and wrinkling. Simultaneously, the invention features embossed recesses of varying depths in different areas, significantly increasing the absorption and dispersion of stress at the wound point, resulting in a marked improvement in wrinkle resistance and cycle performance, which is beneficial for the large-scale application of wound positive electrode sheets.

[0006] Preferably, the thickness of the positive electrode sheet in the second coating area is 90-95% of the thickness of the positive electrode sheet in the first coating area; for example, the thickness of the positive electrode sheet in the second coating area is 90%, 91%, 92%, 93%, 94%, or 95% of the thickness of the positive electrode sheet in the first coating area. If the positive electrode material layer in the second coating area is too thick, the anti-wrinkle effect of the positive electrode sheet is poor; if the positive electrode material layer in the second coating area is too thin, it is easy to break during pressing and will affect the performance of the positive electrode sheet. The preferred thickness ratio has a good anti-wrinkle effect and the electrode sheet is not easy to break during pressing.

[0007] Preferably, the thickness of the positive electrode material layer is 50-300 μm; for example, the thickness of the positive electrode material layer can be 50 μm, 100 μm, 150 μm, 200 μm, 250 μm or 300 μm; the preferred thickness of the positive electrode material layer results in better electrical performance of the positive electrode.

[0008] Preferably, the thickness of the positive current collector is 3~30μm; for example, the thickness of the positive current collector can be 3μm, 5μm, 10μm, 15μm, 20μm, 25μm or 30μm; the preferred thickness of the positive current collector results in better electrical performance of the positive current collector.

[0009] Preferably, the positive electrode current collector is aluminum foil; aluminum foil, as a positive electrode current collector, has good electrical performance, low cost, and a wide range of raw material sources.

[0010] Preferably, the thickness of the second coating area gradually increases along the winding direction of the positive electrode sheet; the preferred thickness variation results in better anti-wrinkle effect and superior electrical performance of the positive electrode sheet.

[0011] Preferably, the recessed embossing is spherical, octagonal, or dodecagonal. Preferred recessed embossing shapes are easier to process, have more regular shapes, absorb and release stress more evenly, have lower cell wrinkling, more cycle life, and better rate performance. Most preferably, the recessed embossing is spherical with a diameter of 2-5 mm. Too small a diameter will result in excessive pressure on the electrode, causing electrode failure and affecting cell performance; too large a diameter will cause the embossing shape to become non-spherical, resulting in poor stress absorption and release, thus affecting the wrinkle reduction effect and lowering cell performance. For example, the diameter of the recessed embossing can be 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, or 5.0 μm.

[0012] Furthermore, the present invention also proposes a method for preparing a wrinkle-resistant wound positive electrode sheet, comprising the following steps: (1) The positive electrode slurry is coated on both sides of the positive electrode current collector to form a positive electrode coating, thereby obtaining a positive electrode sheet semi-finished product; (2) The positive electrode semi-finished product is cold-pressed and embossed to obtain the wound positive electrode finished product.

[0013] Preferably, in step (1), the positive electrode slurry is one of the positive electrode slurry systems of lithium cobalt oxide, ternary, lithium manganese oxide and lithium iron phosphate; the preferred positive electrode slurry has better electrical performance.

[0014] Preferably, in step (1), the coating is carried out using a transfer coating machine; the preferred coating equipment has good coating effect, high efficiency, and adjustable coating thickness.

[0015] Preferably, in step (2), the pressure of the cold pressing process is 0.1~0.35 MPa; the preferred cold pressing pressure results in a moderate density of the positive electrode material layer and better electrical performance.

[0016] Preferably, in step (2), the embossing process is segmented embossing, with the embossing pressure of the first coating area being 0.2~0.65 MPa and the embossing pressure of the second coating area being 0.05~0.55 MPa; by using different pressures for embossing, the positive electrode sheet obtained has better electrical and mechanical properties.

[0017] Preferably, in step (2), during the cold pressing and embossing process, a roller with an uneven surface can be used for cold pressing, and embossing can be formed at the same time as cold pressing; two rollers can be used simultaneously, one is a flat roller for cold pressing, and the other is a roller with an uneven surface for embossing; the electrode sheet can be cold pressed first, then embossed in the second coating area, and finally embossed in the first coating area during winding; the specific cold pressing and embossing process is based on the ability to form a positive electrode sheet that meets the design requirements, and various existing cold pressing and embossing processes can be selected and combined according to the actual situation.

[0018] Preferably, in step (2), cold pressing and embossing are performed simultaneously; the preferred processing technology has higher production efficiency and can shorten the production cycle without affecting the performance of the positive electrode sheet, which is conducive to reducing energy consumption and production costs.

[0019] Furthermore, the present invention also proposes a wrinkle-resistant wound core; the core includes a winding needle and a positive electrode sheet, a negative electrode sheet, and a diaphragm wound on the winding needle; the diaphragm is disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet is the aforementioned wrinkle-resistant wound positive electrode sheet.

[0020] Preferably, the width d of the first coating area on the positive electrode current collector is... n =d1+(n-1)*(a+b+c;The width L of the non-coated area n =L1+3.14 * n *(a+b+c;where, d1 is the width of the first turn of the positive electrode sheet; L1=0~1mm; n is the number of winding layers; a is the thickness of the positive electrode sheet; b is the thickness of the negative electrode sheet; c is the thickness of the separator; the preferred coating area width can better reduce the stress during winding and better reduce the generation of electrode wrinkles.

[0021] Preferably, the thickness of the positive electrode sheet is 10~800μm; for example, the thickness of the positive electrode sheet can be 10μm, 50μm, 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm or 800μm; more preferably, the thickness of the positive electrode sheet is 100~200μm; the preferred electrode sheet thickness results in better electrical and mechanical properties of the core.

[0022] Preferably, the thickness of the negative electrode sheet is 10~800μm; for example, the thickness of the negative electrode sheet can be 10μm, 50μm, 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm or 800μm; more preferably, the thickness of the negative electrode sheet is 100~200μm; the preferred electrode sheet thickness results in better electrical and mechanical properties of the core.

[0023] Preferably, the thickness of the diaphragm is 3~50μm; for example, the thickness of the diaphragm can be 3μm, 5μm, 10μm, 20μm, 30μm, 40μm or 50μm; the preferred diaphragm thickness results in better electrical and mechanical properties of the core.

[0024] Preferably, at least one side of the diaphragm is provided with an adhesive layer; the adhesive layer can better bond the positive and negative electrode sheets, resulting in better electrical performance of the core.

[0025] Preferably, the diaphragm is a PE / PP base film; the preferred diaphragm type has better electrical properties and better core performance.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The positive electrode sheet of the present invention is covered with a positive electrode material layer on the positive electrode current collector, thereby avoiding the loss of energy density caused by the absence of a positive electrode material layer on the positive electrode current collector due to intermittent coating, and can effectively improve the energy density and cycle life of the positive electrode sheet.

[0027] 2. The positive electrode material layer on the positive electrode sheet of the present invention has different thicknesses, so that after winding, the thickness of the electrode sheet at the winding point is less than the thickness of the electrode sheet at other locations. After winding, the gap at the winding point of the core will be larger than the gap on the main body surface. Thus, after the electrode sheet expands due to heat, it can provide extra stress release space at the winding point, ensuring the uniformity of internal stress of the cell, thereby ensuring the flatness of the core and the electrode sheet, and better reducing the deformation of the core and the wrinkling of the electrode sheet.

[0028] 3. The recessed embossed structure provided on the positive electrode sheet of the present invention can better absorb and disperse the stress generated at the winding point of the positive electrode sheet during production and use, thereby effectively preventing the generation of electrode sheet wrinkles and playing a positive role in improving electrode sheet performance and lifespan.

[0029] 4. The embossed structure on the positive electrode sheet of the present invention has different depths in different regions, which significantly increases the absorption and dispersion of stress at the winding point of the positive electrode sheet, thus significantly improving the anti-wrinkle and cycle performance of the electrode sheet, which is conducive to the large-scale application of wound positive electrode sheets.

[0030] 5. The preparation method of the positive electrode sheet of the present invention is simple and reliable. The preparation process can be adjusted according to the actual production situation, which can effectively increase production efficiency, save production costs, and facilitate the large-scale production of positive electrode sheets.

[0031] 6. After the core of the present invention is made into a finished battery cell, the wrinkling problem at the winding point is greatly improved during the cycle process, and the cycle performance is also significantly improved. After disassembling the cycled battery cell, the winding point does not show lithium plating and blackening phenomenon compared with the normal electrode sheet, and the battery cell has better reliability. Attached Figure Description

[0032] Figure 1 This is a front view schematic diagram of the positive electrode sheet in Embodiment 1 of the present invention; Figure 2 This is a cross-sectional schematic diagram of the positive electrode sheet in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the core structure in Embodiment 1 of the present invention; The markings in the diagram are: 1-First coating area; 2-Second coating area; 3-Indented embossing; 4-Positive current collector; 5-Positive electrode material layer; 6-Positive electrode sheet; 7-Separator; 8-Negative electrode sheet; 9-Hand coil. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings.

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Example 1 A wrinkle-resistant wound positive electrode sheet, such as Figure 1 , 2As shown, it consists of a positive current collector 4 (aluminum foil with a thickness of 10μm) and a positive electrode material layer 5 (lithium iron phosphate positive electrode) covering both sides of the positive current collector; the positive electrode material 5 is divided into 4 first coating areas 1 and 3 second coating areas 2; the thickness of the second coating area 2 is 190μm (200*95%) (the thickness of the positive electrode material layer 5 is 180μm), and the electrode thickness of the first coating area 1 is 200μm (the thickness of the positive electrode material layer 5 is 190μm); the second coating area 2 corresponds to the bending part when the positive electrode sheet is wound; the width of the first first coating area is 5.0mm (that is, the width of the winding needle 9, the design size is 5mm), the width of the second first coating area is 5.41mm (5+1*(0.2+0.2+0.01)), and the width of the third first coating area is 5.82mm (5+2*(0.2+0.2+0.01)). The width of the fourth first coating area is 6.23mm (5+3*(0.2+0.2+0.01)), the width of the first second coating area (L1=0.5mm) is 1.756mm (0.5+3.14*1*(0.2+0.19+0.01)), and the width of the second second coating area is 3.012mm (0.5+3.14*2*(0.2+0.01)). 19+0.01), the width of the third second coating area is 4.268mm (0.5+3.14*3*(0.2+0.19+0.01)); the positive electrode material layer 5 is provided with recessed embossing 3 (spherical, with a diameter of 3mm, the embossing depth on the second coating area 2 is 11.4μm (190*6%); the embossing depth on the first coating area 2 is 16μm (200*8%)).

[0036] Specific preparation method: (1) The lithium iron phosphate positive electrode slurry is coated on both sides of the positive electrode current collector using a transfer coating machine to form a positive electrode coating, thereby obtaining a positive electrode semi-finished product; (2) The positive electrode semi-finished product is cold-pressed on the second coating area using a roller with an uneven surface (pressure of 0.35 MPa), and embossing is formed at the same time as cold pressing; then the first coating area is embossed during winding (pressure of 0.35 MPa) to obtain the wound positive electrode finished product.

[0037] A wrinkle-resistant wound core is made using the aforementioned wrinkle-resistant wound positive electrode sheet, such as... Figure 3 As shown, the core includes a winding needle 9 and a positive electrode 6, a negative electrode 8 (graphite, 200μm) and a separator 7 (10μm) wound on the winding needle 9; the separator 7 is disposed between the positive electrode 6 and the negative electrode 8.

[0038] Example 2 A wrinkle-resistant wound positive electrode sheet comprises a positive current collector 4 (aluminum foil with a thickness of 10 μm) and a positive electrode material layer 5 (lithium iron phosphate positive electrode) covering both sides of the positive current collector; the positive electrode material 5 is divided into four first coating areas 1 and three second coating areas 2; the thickness of the second coating area 2 is 180 μm (200*90%) (the thickness of the positive electrode material layer 5 is 170 μm), and the electrode sheet thickness of the first coating area 1 is 200 μm (the thickness of the positive electrode material layer 5 is 190 μm); the second coating area 2 corresponds to the bending part during the winding of the positive electrode sheet; the width of the first first coating area is 5.0 mm (i.e., the width of the winding needle 9, designed size is 5 mm), the width of the second first coating area is 5.41 mm (5+1*(0.2+0.2+0.01)), and the width of the third first coating area is 5.82 mm (5+2*(0.2)). The width of the fourth first coating area is 6.23mm (5 + 3 * (0.2 + 0.2 + 0.01)), the width of the first second coating area (L1 = 0.5mm) is 1.725mm (0.5 + 3.14 * 1 * (0.2 + 0.18 + 0.01)), and the width of the second second coating area is 2.449mm (0.5 + 3.14 * 2 * (0.2 + 0.2 + 0.01)). +0.18+0.01)), the width of the third second coating area is 4.174mm (0.5+3.14*3*(0.2+0.18+0.01)); the positive electrode material layer 5 is provided with recessed embossing 3 (spherical, with a diameter of 3mm, the embossing depth on the second coating area 2 is 10.8μm (180*6%); the embossing depth on the first coating area 2 is 16μm (200*8%)).

[0039] Specific preparation method: (1) The lithium iron phosphate positive electrode slurry is coated on both sides of the positive electrode current collector using a transfer coating machine to form a positive electrode coating, thereby obtaining a positive electrode semi-finished product; (2) The positive electrode semi-finished product is rolled on the second coating area simultaneously by two rollers. One is a flat roller for cold pressing (pressure of 0.1 MPa), and the other is a roller with an uneven surface for embossing (0.2 MPa). Then, the first coating area is embossed during winding (pressure of 0.2 MPa) to obtain the finished wound positive electrode.

[0040] A wrinkle-resistant wound core is made using the above-mentioned wrinkle-resistant wound positive electrode sheet. The core includes a winding needle 9 and a positive electrode sheet 6, a negative electrode sheet 8 (graphite, 200μm) and a separator 7 (10μm) wound on the winding needle 9. The separator 7 is disposed between the positive electrode sheet 6 and the negative electrode sheet 8.

[0041] Example 3 A wrinkle-resistant wound positive electrode sheet comprises a positive current collector 4 (aluminum foil with a thickness of 10 μm) and a positive electrode material layer 5 (lithium iron phosphate positive electrode) covering both sides of the positive current collector; the positive electrode material 5 is divided into four first coating areas 1 and three second coating areas 2; the thickness of the second coating areas 2 is 184 μm (200*92%) (the thickness of the positive electrode material layer 5 is 174 μm), and the electrode sheet thickness of the first coating areas 1 is 200 μm (the thickness of the positive electrode material layer 5 is 190 μm); the second coating areas 2 correspond to the bending portions during the winding of the positive electrode sheet; the width of the first first coating area is 5.0 mm. mm (i.e., the width of the coil needle 9, designed size is 5mm), the width of the second first coating area is 5.41mm (5+1*(0.2+0.2+0.01)), the width of the third first coating area is 5.82mm (5+2*(0.2+0.2+0.01)), the width of the fourth first coating area is 6.23mm (5+3*(0.2+0.2+0.01)), the width of the first second The width of the first coating area (L1=0.5mm) is 1.737mm (0.5+3.14*1*(0.2+0.184+0.01)), the width of the second coating area is 2.974mm (0.5+3.14*2*(0.2+0.184+0.01)), and the width of the third second coating area is 4.211mm (0.5+3.14*3*(0.2+0.184+0.01)). The positive electrode material layer 5 is provided with recessed embossing 3 (spherical, with a diameter of 3mm, the embossing depth on the second coating area 2 is 11.4μm (184*6%), and the embossing depth on the first coating area 2 is 16μm (200*8%)).

[0042] Specific preparation method: (1) The lithium iron phosphate positive electrode slurry is coated on both sides of the positive electrode current collector using a transfer coating machine to form a positive electrode coating, thereby obtaining a positive electrode semi-finished product; (2) The positive electrode semi-finished product is first cold-pressed (pressure is 0.35 MPa), then embossed in the second coating area (pressure is 0.65 MPa), and finally embossed in the first coating area during winding (pressure is 0.55 MPa) to obtain the finished wound positive electrode.

[0043] A wrinkle-resistant wound core is made using the above-mentioned wrinkle-resistant wound positive electrode sheet. The core includes a winding needle 9 and a positive electrode sheet 6, a negative electrode sheet 8 (graphite, 200μm) and a separator 7 (10μm) wound on the winding needle 9. The separator 7 is disposed between the positive electrode sheet 6 and the negative electrode sheet 8.

[0044] Comparative Example 1 A type of wound positive electrode sheet, which differs from Example 1 only in that the second coating area 2 is a blank layer (i.e. there is no positive electrode material layer there) and there is no recessed embossing there.

[0045] A wound core is made using the above-mentioned wound positive electrode sheet. The core includes a winding needle 9 and a positive electrode sheet 6, a negative electrode sheet 8 (200μm) and a separator 7 (10μm) wound on the winding needle 9. The separator 7 is disposed between the positive electrode sheet 6 and the negative electrode sheet 8.

[0046] Comparative Example 2 A wound positive electrode sheet differs from Example 1 only in that the thickness of the positive electrode material layer is exactly the same, that is, the electrode sheet thickness is 200μm (the thickness of the positive electrode material layer is 190μm), and the embossing depth is the same (16μm).

[0047] A wound core is made using the above-mentioned wound positive electrode sheet. The core includes a winding needle 9 and a positive electrode sheet 6, a negative electrode sheet 8 (200μm) and a separator 7 (10μm) wound on the winding needle 9. The separator 7 is disposed between the positive electrode sheet 6 and the negative electrode sheet 8.

[0048] Comparative Example 3 A type of wound positive electrode sheet, which differs from Example 1 only in that neither the second coating area 2 nor the first coating area 1 has a recessed embossing.

[0049] A wound core is made using the above-mentioned wound positive electrode sheet. The core includes a winding needle 9 and a positive electrode sheet 6, a negative electrode sheet 8 (200μm) and a separator 7 (10μm) wound on the winding needle 9. The separator 7 is disposed between the positive electrode sheet 6 and the negative electrode sheet 8.

[0050] Comparative Example 4 A type of wound positive electrode sheet, which differs from Example 1 only in that the second coating area 2 has no recessed embossing.

[0051] A wound core is made using the above-mentioned wound positive electrode sheet. The core includes a winding needle 9 and a positive electrode sheet 6, a negative electrode sheet 8 (200μm) and a separator 7 (10μm) wound on the winding needle 9. The separator 7 is disposed between the positive electrode sheet 6 and the negative electrode sheet 8.

[0052] Comparative Example 5 A type of wound positive electrode sheet, which differs from Example 1 only in that the first coating area 1 has no recessed embossing.

[0053] A wound core is made using the above-mentioned wound positive electrode sheet. The core includes a winding needle 9 and a positive electrode sheet 6, a negative electrode sheet 8 (200μm) and a separator 7 (10μm) wound on the winding needle 9. The separator 7 is disposed between the positive electrode sheet 6 and the negative electrode sheet 8.

[0054] Blank Group 1 A type of wound positive electrode sheet, which differs from Example 1 in that: the thickness of the positive electrode material layer is the same (95μm), and there is no embossed pattern.

[0055] A wound core is made using the above-mentioned wound positive electrode sheet. The core includes a winding needle 9 and a positive electrode sheet 6, a negative electrode sheet 8 (200μm) and a separator 7 (10μm) wound on the winding needle 9. The separator 7 is disposed between the positive electrode sheet 6 and the negative electrode sheet 8.

[0056] Experiment Example 1: The Influence of Electrode Structure on Core Performance The cell cores of Examples 1-3, Comparative Examples 1-5, and Blank Group 1 were tested for cell wrinkling degree, number of cycles (25℃, 80% SOH), and cell rate performance (3C / 1C) (20 samples were randomly selected from each group, and the average value was taken). The test results are as follows: Experiment Example 2: Embossing Shape Experiment The electrode sheets and cores with the same structure and dimensions as those in Example 1 were used, with the only differences being: the embossing depth was 8% of the electrode thickness; the embossing area was the same (a circle with a diameter of 3 mm); the embossing shape was different; the cell wrinkling degree, cycle number (25℃, 80% SOH), and cell rate performance (3C / 1C) of the core were tested (20 samples were randomly selected from each group, and the average value was taken). The results are as follows: The results of Experiment Example 2 show that the shape of the recessed embossing has a certain impact on the electrical performance of the core, especially on the number of cycles. The embossing shape has a significant impact on the degree of wrinkling of the core. Among them, the spherical, octagonal or dodecagonal recessed embossing results in a core with significantly better wrinkle resistance and number of cycles than other shapes, and the cell rate performance is also better.

[0057] Experiment Example 3: Embossing Depth Experiment The electrode sheets and cores with the same structure and dimensions as those in Example 1 were used, with the only differences being: the thickness of the positive electrode sheet was 200 μm (first coating area), and the thickness of the electrode sheet in the second coating area 2 was 190 μm; the depth of the embossing was different; the degree of cell wrinkling and the number of cycles (25℃, 80% SOH) of the core were tested (20 samples randomly selected from each group, average value was taken), and the results are as follows: The results of Experiment Example 3 show that the embossing depth has a significant impact on the degree of wrinkling and the number of cycles of the core. Specifically, when the embossing depth exceeds 10% of the electrode thickness, the over-compression (exceeding the upper limit of material compaction) performance of the electrode in the embossed area will be significantly reduced. When the embossing depth is less than 5% of the electrode thickness, it can improve the wrinkling of the cell to some extent, but the improvement in cycle performance is not significant. When the embossing depth of the normal coating area is 5-10% of the electrode thickness, and the embossing depth of the non-coating area is 5-8% of the electrode thickness, the embossing depth has a significant effect on reducing the wrinkling degree of the cell and improving the cycle performance.

[0058] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wrinkle-resistant wound positive electrode sheet, characterized in that, The device includes a positive current collector (4) and a positive electrode material layer (5) covering the positive current collector; the positive electrode material layer (5) is divided into a first coating area (1) and a second coating area (2), the thickness of the second coating area (2) is less than the thickness of the first coating area (1); the second coating area (2) corresponds to the bend during the winding of the positive electrode sheet; the width of the first coating area (1) and the second coating area (2) gradually increases along the winding direction from the starting point of the positive electrode sheet winding; the width dn of the first coating area (1) on the positive current collector (4) is d1 + (n-1) * (a+b+c); Second The width of the coating area (2) is Ln = L1 + 3.14* n*(a+b+c); where d1 is the width of the first turn of the positive electrode sheet; L1=0~1mm; n is the number of winding layers; a is the thickness of the positive electrode sheet; b is the thickness of the negative electrode sheet; c is the thickness of the separator; the thickness of the second coating area (2) gradually increases along the winding direction of the positive electrode sheet, and the positive electrode material layer (5) is also provided with recessed embossing (3), and the depth of the recessed embossing (3) in the first coating area (1) is 5~10% of the corresponding electrode sheet thickness, and the depth of the recessed embossing (3) in the second coating area (2) is 5~8% of the corresponding electrode sheet thickness.

2. The wound positive electrode sheet according to claim 1, characterized in that, The thickness of the positive electrode in the second coating area (2) is 90-95% of the thickness of the positive electrode in the first coating area (1).

3. The wound positive electrode sheet according to claim 1, characterized in that, The thickness of the positive electrode material layer (5) is 50-300 μm; and / or the thickness of the positive electrode current collector (4) is 3-30 μm.

4. The wound positive electrode sheet according to any one of claims 1-3, characterized in that, The recessed embossing (3) is spherical, octagonal or dodecagonal.

5. A method for preparing the anti-wrinkle wound positive electrode sheet according to any one of claims 1-4, comprising the following steps: (1) The positive electrode slurry is coated on both sides of the positive electrode current collector to form a positive electrode coating, thereby obtaining a positive electrode sheet semi-finished product; (2) The positive electrode semi-finished product is first cold-pressed and then embossed to obtain the finished positive electrode coil.

6. The preparation method according to claim 5, characterized in that, In step (2), the pressure of the cold pressing process is 0.1~0.35 MPa.

7. The preparation method according to claim 5 or 6, characterized in that, In step (2), the embossing process is segmented embossing, with the embossing pressure of the first coating area being 0.2~0.65 MPa and the embossing pressure of the second coating area being 0.05~0.55 MPa.

8. A wrinkle-resistant wound core, the core comprising a winding needle (9) and a positive electrode plate (6), a negative electrode plate (8), and a diaphragm (7) wound on the winding needle (9); the diaphragm (7) being disposed between the positive electrode plate (6) and the negative electrode plate (7); characterized in that, The positive electrode (6) is the anti-wrinkle wound positive electrode as described in any one of claims 1-4.

9. The anti-wrinkle wound core according to claim 8, characterized in that, The thickness of the positive electrode (6) is 10~800μm; and / or the thickness of the negative electrode (8) is 10~800μm; and / or the thickness of the separator (7) is 3~50μm.

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