Electrode assembly, preparation method and battery

Abstract

The invention provides an electrode assembly, a preparation method and a battery, the electrode assembly comprises a positive plate, a negative plate and a diaphragm, the positive plate comprises a positive current collector and a positive active material layer, the positive active material layer comprises a first region and a second region, the first region is located at a winding inner ring of the positive plate, and the second region is located at a winding outer ring of the positive plate; a plurality of etching lines are arranged in the first region of the positive active material layer; the second area of the positive plate is provided with a plurality of embossments; according to the invention, etching is carried out in the first region, the slot position of the etching line can increase the liquid retention amount, and meanwhile, the N / P value of the roll core and the CB value of the arc region can be increased, so that lithium precipitation of the pole piece is avoided; the second region is embossed, the embossed pattern can effectively improve the thickness and the density of the positive electrode active material layer of the positive electrode plate, the embossed pattern can improve the gram volume exertion of the positive electrode under large surface density, and the embossed pattern can store more electrolyte, increase more contact areas and lithium removal channels, effectively improve the double discharge capacity and the dynamic performance and improve the first effect of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of high energy density batteries, and in particular to an electrode assembly and a preparation method thereof, and a battery. Background Art As the demand for energy density in the consumer market increases. Silicon-carbon materials are currently the mainstream development materials, but the design and development of high energy density requires a higher silicon content and a higher surface density of the positive electrode coating. A higher surface density means a thicker electrode sheet. Thick electrodes will increase the lithium ion charge transfer resistance, increase the lithium ion transmission path, and significantly deteriorate the system dynamics. When performing fast charging tests, fast charging will cause local potential imbalance and lithium enrichment, leading to lithium precipitation. Therefore, it is necessary to reduce the polarization of high energy density batteries in the fast charging format, and it is necessary to improve the dynamics of the positive electrode sheet. At the same time, for high energy density systems, the liquid retention capacity of the positive electrode sheet has always been very low, which makes it easy to dive during long cycle periods, and the liquid retention performance of the battery cell also needs to be improved. Therefore, how to overcome the above-mentioned technical problems and defects has become a key issue that needs to be solved. Summary of the invention

[0002] In view of the problems of increased lithium ion charge transfer resistance in the positive electrode sheet, significant deterioration of system dynamics, local potential imbalance leading to lithium precipitation, and low liquid retention capacity in current high energy density batteries, the present invention provides an electrode assembly, a preparation method, and a battery.

[0003] The technical solution adopted by the present invention to solve the above technical problems is as follows: A first aspect of the present invention provides an electrode assembly, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form the electrode assembly; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on at least one side of the surface of the positive electrode current collector, and the single surface density of the positive electrode active material layer is 120 g / m 2 ~300g / m 2 ; The positive electrode active material layer includes a first region and a second region, the first region is located in the inner winding circle of the positive electrode sheet, and the second region is located in the outer winding circle of the positive electrode sheet; along a direction parallel to the thickness of the positive electrode sheet, the first region of the positive electrode active material layer is provided with multiple etching lines; the second region of the positive electrode sheet is provided with multiple embossings.

[0004] Optionally, the number of winding folds of the first region is 1 / 4-1 / 2 of the total number of winding folds of the positive electrode sheet.

[0005] Optionally, the sum of the volumes of the etched areas of all the etched lines is 1%-2% of the volume of the positive electrode active material layer.

[0006] Optionally, the depth of the etching line is 25% to 40% of the thickness of the positive electrode active material layer; the spacing between two adjacent etching lines is 0.5 mm to 1.5 mm; and the width of the etching line is 60 μm to 105 μm.

[0007] Optionally, the depth of the etching line is 30% to 35% of the thickness of the positive electrode active material layer; the spacing between two adjacent etching lines is 0.8 mm to 1.2 mm; and the width of the etching line is 75 μm to 90 μm.

[0008] Optionally, the number of winding folds of the second region is 1 / 2-3 / 4 of the total number of winding folds of the positive electrode sheet.

[0009] Optionally, the total volume of all the embossed areas is 1.5%-7% of the volume of the positive electrode active material layer.

[0010] Optionally, the embossing area accounts for 10% to 50% of the area of ​​the second region.

[0011] Optionally, along a direction parallel to the thickness of the positive electrode sheet, the depth of the embossing is 2%-10% of the thickness of the positive electrode active material layer.

[0012] Optionally, the single surface density of the positive electrode active material layer is 200 g / m 2 ~300g / m 2 ; The negative electrode sheet precursor comprises a negative electrode current collector and a negative electrode active material layer coated on at least one side of the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material and CMC; The negative electrode sheet precursor is subjected to high temperature treatment to obtain the negative electrode sheet, so that the CMC in the negative electrode active material layer is carbonized to form conductive carbon black.

[0013] Optionally, the temperature of the high temperature treatment of the negative electrode sheet precursor is 200° C. to 300° C., and the time of the high temperature treatment of the negative electrode sheet precursor is 3-7 hours.

[0014] Optionally, the negative electrode active material includes a silicon-carbon material, wherein the silicon content accounts for 3-15% of the mass of the silicon-carbon material.

[0015] A second aspect of the present invention provides a method for preparing an electrode assembly, comprising the following steps: S1. Obtain a positive electrode sheet, a negative electrode sheet and a separator; S2. etching a plurality of etching lines in a first region of the positive active material layer of the positive electrode sheet, and embossing in a second region of the positive active material layer of the positive electrode sheet; S3. Stack and wind the positive electrode sheet, the separator and the negative electrode sheet in sequence to form an electrode assembly; so that the first region is located in the inner winding circle of the positive electrode sheet, and the second region is located in the outer winding circle of the positive electrode sheet.

[0016] A third aspect of the present invention provides a battery, comprising a battery housing, an electrolyte, and the electrode assembly as described above, or an electrode assembly prepared by the method for preparing the electrode assembly as described above.

[0017] According to the electrode assembly provided by the present invention, by etching and marking the first area of ​​the positive electrode active material layer of the inner circle of the core, the grooves of the etching lines can increase the liquid retention amount, and at the same time can increase the N / P value of the core, and make up for the N / P value loss of the inner circle of the core; at the same time, the CB value of the arc area of ​​the positive electrode sheet can be significantly increased, avoiding the problem of lithium deposition caused by the low CB value of the electrode sheet, and the liquid retention amount increased by the grooves of the etching lines can improve the lithium deposition problem in the arc area of ​​the core, and by embossing the second area of ​​the positive electrode active material layer of the outer circle of the core, embossing can effectively improve the thickness and density of the positive electrode active material layer of the positive electrode sheet, embossing can improve the positive electrode specific capacity under large surface density, embossing can store more electrolyte, increase more contact area, increase lithium desorption channels, effectively improve the discharge capacity of the core and the dynamic performance of the core, and improve the first effect of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 is a schematic cross-sectional view of a positive electrode sheet provided in one embodiment of the present invention; Figure 2 is a schematic top view of a positive electrode sheet provided by an embodiment of the present invention; Figure 3 is a schematic cross-sectional view of a negative electrode sheet precursor provided by one embodiment of the present invention; Figure 4 is a schematic cross-sectional view of a negative electrode sheet provided by one embodiment of the present invention; Figure 5 is a cross-sectional schematic diagram of an electrode assembly provided by an embodiment of the present invention; The reference numerals in the drawings of the specification are as follows: 100-electrode assembly; 1-positive electrode sheet; 11-positive electrode current collector; 12-positive electrode active material layer; 121-first region; 1211-etching line; 122-second region; 1221-embossing; 2-negative electrode sheet; 21-negative electrode current collector; 22-negative electrode active material layer; 221-CMC; 3-diaphragm. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] In the description of the present invention, it should be understood that the terms "longitudinal", "radial", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0022] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0025] like Figure 1-Figure 2As shown, in one embodiment, the first aspect of the present invention provides an electrode assembly 100, comprising a positive electrode sheet 1, a negative electrode sheet 2 and a separator 3, wherein the positive electrode sheet 1, the separator 3 and the negative electrode sheet 2 are stacked and wound to form the electrode assembly 100; The positive electrode sheet 1 includes a positive electrode current collector 11 and a positive electrode active material layer 12 coated on at least one side of the surface of the positive electrode current collector 11. The single surface density of the positive electrode active material layer 12 is 120 g / m 2 ~300g / m 2 ; The positive electrode active material layer 12 includes a first region 121 and a second region 122, the first region 121 is located at the inner winding circle of the positive electrode sheet 1, and the second region 122 is located at the outer winding circle of the positive electrode sheet 1; along the thickness direction parallel to the positive electrode sheet 1, the first region 121 of the positive electrode active material layer 12 is provided with multiple etching lines 1211; the second region 122 of the positive electrode sheet 1 is provided with multiple embossings 1221.

[0026] In the conventional wound core structure, the current density in the inner circle of the core is relatively large, the polarization is relatively large, and the winding tension of the inner circle of the core is relatively large, which can easily cause the problem of low N / P value of the core; moreover, the curvature of the arc area of ​​the positive electrode sheet 1 is large, resulting in a low CB value at this time.

[0027] In one embodiment, the present invention etches and marks the first area 121 of the positive electrode active material layer 12 of the inner circle of the winding core. The groove position of the etching line 1211 can increase the liquid retention amount and increase the N / P value of the winding core, thereby compensating for the N / P value loss of the inner circle of the winding core. At the same time, the CB value of the arc area of ​​the positive electrode sheet 1 can be significantly increased to avoid lithium deposition problems caused by the low CB value of the electrode sheet. Moreover, the increased liquid retention amount of the groove position of the etching line 1211 can improve the lithium deposition problem in the arc area of ​​the winding core.

[0028] Furthermore, the length of the etched line 1211 is the same as the width of the first region 121 , or the length of the etched line 1211 is slightly smaller than the width of the first region 121 , thereby facilitating the increase of liquid retention in the groove of the etched line 1211 .

[0029] In one embodiment, the present invention performs embossing 1221 treatment on the second area 122 of the positive electrode active material layer 12 of the outer circle of the winding core. The embossing 1221 can effectively improve the thickness and density of the positive electrode active material layer 12 of the positive electrode sheet 1, and the embossing 1221 can improve the positive electrode specific capacity under large surface density. The embossing 1221 can store more electrolyte, increase more contact area, increase lithium desorption channels, effectively improve the discharge capacity and dynamic performance of the winding core, and improve the first effect of the battery.

[0030] Specifically, the embossing 1221 is formed by rolling the second region 122 of the positive electrode active material layer 12 with an embossing roller, and the shape of the embossing 1221 is any one of a circle, a square, a diamond, a triangle, a hexagon, a trapezoid or an ellipse; in a preferred embodiment, the shape of the embossing 1221 is a circle.

[0031] like Figure 1-Figure 2 As shown, in one embodiment, the number of winding folds of the first region 121 is 1 / 4-1 / 2 of the total number of winding folds of the positive electrode sheet 1 .

[0032] Specifically, the number of winding folds of the first region 121 is any point value among 1 / 4, 3 / 10, 7 / 20, 2 / 5, 9 / 20 or 1 / 2 of the total number of winding folds of the positive electrode sheet 1, or a range value consisting of any two point values; in a preferred embodiment, the number of winding folds of the first region 121 is 3 / 10-9 / 20 of the total number of winding folds of the positive electrode sheet 1.

[0033] When the winding number of the first region 121 is 1 / 4-1 / 2 of the total winding number of the positive electrode sheet 1, the high capacity of the core can be maintained while taking into account the long cycle performance of the core, and the lithium deposition problem in the arc zone of the positive electrode sheet 1 can be effectively improved; when the winding number of the first region 121 is less than 1 / 4 of the total winding number of the positive electrode sheet 1, the CB value of the arc zone of the positive electrode sheet 1 does not change significantly, and the lithium deposition in the arc zone is not improved significantly; when the winding number of the first region 121 is greater than 1 / 2 of the total winding number of the positive electrode sheet 1, the CB value of the arc zone of the positive electrode sheet 1 will be too large, resulting in a large loss of core capacity.

[0034] like Figure 1-Figure 2 As shown, in one embodiment, the total volume of the etched areas of all etched lines 1211 is 1%-2% of the volume of the positive electrode active material layer 12 .

[0035] Specifically, the sum of the volumes of the etched areas of all etched lines 1211 is any one of 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2% of the volume of the positive electrode active material layer 12, or a range of any two values. In a preferred embodiment, the sum of the volumes of the etched areas of all etched lines 1211 is 1.2%-1.8% of the volume of the positive electrode active material layer 12.

[0036] Specifically, when the sum of the volumes of the etched areas of all the etched lines 1211 is 1%-2% of the volume of the positive electrode active material layer 12, the high capacity of the core can be maintained while taking into account the long cycle performance of the core, and the lithium plating problem in the arc area of ​​the positive electrode sheet 1 can be effectively improved; when the sum of the volumes of the etched areas of all the etched lines 1211 is less than 1% of the volume of the positive electrode active material layer 12, the CB value of the arc area of ​​the positive electrode sheet 1 does not change significantly, and the lithium plating in the arc area is not improved significantly; when the sum of the volumes of the etched areas of all the etched lines 1211 is greater than 2% of the volume of the positive electrode active material layer 12, the CB value of the arc area of ​​the positive electrode sheet 1 will be too large, resulting in a large loss of core capacity.

[0037] like Figure 1-Figure 2 As shown, in one embodiment, the depth of the etching line 1211 is 25% to 40% of the thickness of the positive electrode active material layer 12; the spacing between two adjacent etching lines 1211 is 0.5 mm to 1.5 mm; and the width of the etching line 1211 is 60 μm to 105 μm.

[0038] Specifically, the depth of all etching lines 1211 is any point value among 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% or 40% of the thickness of the positive electrode active material layer 12, or a range value consisting of any two point values.

[0039] Specifically, when the depth of the etching line 1211 is 25% to 40% of the thickness of the positive electrode active material layer 12, it can maintain the high capacity of the core while taking into account the long cycle performance of the core, and can effectively improve the lithium plating problem in the arc area of ​​the positive electrode sheet 1; when the depth of the etching line 1211 is less than 25% of the thickness of the positive electrode active material layer 12, the current density of the inner circle of the core is relatively large, the polarization is relatively large, and the winding tension of the inner circle of the core is relatively large, which can easily cause the problem of low N / P value of the core; when the depth of the etching line 1211 is greater than 40% of the thickness of the positive electrode active material layer 12, the N / P value of the core increases, but it will cause the high temperature performance of the core to deteriorate, and the capacity loss of the core is obvious.

[0040] Specifically, the spacing between two adjacent etching lines 1211 is any point value among 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm or 1.5mm, or a range value consisting of any two point values.

[0041] Specifically, when the spacing between two adjacent etching lines 1211 is 0.5mm~1.5mm, the high capacity of the core can be maintained while taking into account the long cycle performance of the core, which can effectively improve the lithium plating problem in the negative arc area corresponding to the positive electrode sheet 1; when the spacing between two adjacent etching lines 1211 is less than 0.5mm, the N / P value of the core increases, but it will cause the high temperature performance of the core to deteriorate, and the capacity loss of the core is obvious; when the spacing between two adjacent etching lines 1211 is greater than 1.5mm, the N / P value of the inner core changes less, and the improvement of the negative arc area corresponding to the positive electrode sheet 1 is not obvious, and the capacity is lost.

[0042] Specifically, the width of the etched line 1211 is any point value among 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm or 105 μm, or a range value consisting of any two point values.

[0043] Specifically, when the width of the etching line 1211 is 60μm~105μm, it can maintain the high capacity of the core while taking into account the long cycle performance of the core, and can effectively improve the lithium deposition problem in the arc area of ​​the positive electrode sheet 1; when the width of the etching line 1211 is less than 60μm, the CB value of the negative arc area corresponding to the positive electrode sheet 1 does not change significantly, and the lithium deposition in the arc area is not improved significantly; when the width of the etching line 1211 is greater than 105μm, the CB value of the negative arc area corresponding to the positive electrode sheet 1 will be too large, the core capacity loss will be large, and the high temperature cycle retention rate will deteriorate.

[0044] like Figure 1-Figure 2 As shown, in a preferred embodiment, the depth of the etching line 1211 is 30% to 35% of the thickness of the positive electrode active material layer 12; the spacing between two adjacent etching lines 1211 is 0.8 mm to 1.2 mm; and the width of the etching line 1211 is 75 μm to 90 μm.

[0045] like Figure 1-Figure 2 As shown, in one embodiment, the number of winding folds of the second region 122 is 1 / 2-3 / 4 of the total number of winding folds of the positive electrode sheet 1 .

[0046] Specifically, the number of winding folds of the second region 122 is any point value among 1 / 2, 11 / 20, 3 / 5, 13 / 20, 7 / 10 or 3 / 4 of the total number of winding folds of the positive electrode sheet 1, or a range value consisting of any two point values; in a preferred embodiment, the number of winding folds of the second region 122 is 11 / 20-7 / 10 of the total number of winding folds of the positive electrode sheet 1.

[0047] When the winding number of the second area 122 is 1 / 2-3 / 4 of the total winding number of the positive electrode sheet 1, it can maintain the high capacity of the core while taking into account the long cycle performance of the core, and can effectively improve the lithium plating problem in the arc area of ​​the positive electrode sheet 1; when the winding number of the second area 122 is less than 1 / 2 of the total winding number of the positive electrode sheet 1, it will cause the CB value of the arc area of ​​the positive electrode sheet 1 to be too large and the capacity loss of the core to be large; when the winding number of the second area 122 is greater than 3 / 4 of the total winding number of the positive electrode sheet 1, the CB value of the arc area of ​​the positive electrode sheet 1 does not change significantly, and the improvement of lithium plating in the arc area is not obvious.

[0048] like Figure 1-Figure 2 As shown, in one embodiment, the total volume of all embossed areas 1221 is 1.5%-7% of the volume of the positive electrode active material layer 12 .

[0049] Specifically, the total volume of all the embossing areas 1221 is any point value of 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5% or 7% of the volume of the positive electrode active material layer 12, or a range value consisting of any two point values; in a preferred embodiment, the total volume of all the embossing areas 1221 is 3%-5% of the volume of the positive electrode active material layer 12.

[0050] Specifically, when the sum of the volumes of all embossed areas 1221 is 1.5%-7% of the volume of the positive electrode active material layer 12, the thickness and density of the positive electrode active material layer 12 of the positive electrode sheet 1 can be effectively improved, and the embossing 1221 can improve the positive electrode capacity under large surface density. At the same time, the embossing can reduce the initial thickness of the battery cell and improve the volume energy density. The embossing 1221 can store more electrolyte, increase more contact area, increase the lithium removal channel, effectively improve the discharge capacity of the core and the dynamic performance of the core, and increase the first effect of the battery; when all embossed areas 1221 When the total volume of the area is less than 1.5% of the volume of the positive electrode active material layer 12, the positive electrode sheet 1 cannot effectively improve the storage performance of the electrolyte and improve the arc lithium plating problem; when the total volume of all embossed areas 1221 is greater than 7% of the volume of the positive electrode active material layer 12, the positive electrode sheet is prone to overpressure in the embossed area, and the electrode sheet is prone to break due to excessive embossing torque. At the same time, the overpressure part has low gram capacity. For 9μm aluminum foil, the torque exceeds 300N and the electrode sheet will break. Excessive embossing means that the electrode sheet needs a higher torque to press the electrode sheet down, which can easily cause the aluminum foil to break.

[0051] like Figure 1-Figure 2 As shown, in one embodiment, the area of ​​the embossing 1221 accounts for 10% to 50% of the area of ​​the second region 122.

[0052] Specifically, the area of ​​the embossing 1221 accounts for any point value among 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50% of the area of ​​the second region 122, or a range value consisting of any two point values; in a preferred embodiment, the area of ​​the embossing 1221 accounts for 20%-40% of the area of ​​the second region 122.

[0053] Specifically, when the area of ​​embossing 1221 accounts for 10% to 50% of the area of ​​the second region 122, the thickness and density of the positive active material layer 12 of the positive electrode sheet 1 can be effectively improved, and the embossing 1221 can improve the positive electrode capacity under large surface density. The embossing 1221 can store more electrolyte, increase more contact area, increase lithium removal channels, effectively improve the discharge capacity of the core and the dynamic performance of the core, and improve the first effect of the battery; when the area of ​​embossing 1221 is less than 10% of the area of ​​the second region 122, the positive electrode sheet 1 cannot effectively improve the storage performance of the electrolyte and improve the arc lithium precipitation problem; when the area of ​​embossing 1221 is greater than 50% of the area of ​​the second region 122, the pressure area of ​​the electrode sheet increases. The aluminum foil may break during the cycle, affecting the cycle retention rate.

[0054] like Figure 1-Figure 2 As shown, in one embodiment, along a direction parallel to the thickness of the positive electrode sheet 1 , the depth of the embossing 1221 is 2%-10% of the thickness of the positive electrode active material layer 12 .

[0055] Specifically, the depth of the embossing 1221 is any point value of 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% of the thickness of the positive electrode active material layer 12, or a range value consisting of any two point values; in a preferred embodiment, the depth of the embossing 1221 is 4%-8% of the thickness of the positive electrode active material layer 12.

[0056] Specifically, when the depth of the embossing 1221 is 2%-10% of the thickness of the positive electrode active material layer 12, the thickness and density of the positive electrode active material layer 12 of the positive electrode sheet 1 can be effectively improved, and the embossing 1221 can improve the positive electrode capacity under large surface density. The embossing 1221 can store more electrolyte, increase more contact area, increase lithium removal channels, effectively improve the discharge capacity of the core and the dynamic performance of the core, and improve the first effect of the battery; when the depth of the embossing 1221 is less than the positive electrode When the depth of the embossing 1221 is greater than 2% of the thickness of the active material layer 12, the positive electrode sheet 1 cannot effectively improve the storage performance of the electrolyte and improve the lithium plating problem; when the depth of the embossing 1221 is greater than 10% of the thickness of the positive electrode active material layer 12, the positive electrode sheet is prone to over-pressure in the embossing area, and the electrode sheet is prone to break due to excessive embossing torque. At the same time, the over-pressure part has low gram capacity. When the embossing torque exceeds 300N, the electrode sheet will break. Excessive embossing means that the electrode sheet needs a higher torque to press the electrode sheet down, which can easily cause the aluminum foil to break.

[0057] like Figure 3-Figure 4 As shown, in one embodiment, the single surface density of the positive electrode active material layer 12 is 200 g / m 2 ~300g / m 2 ; The negative electrode sheet 2 precursor includes a negative electrode current collector 21 and a negative electrode active material layer 22 coated on at least one side of the surface of the negative electrode current collector 21, and the negative electrode active material layer 22 includes a negative electrode active material and CMC; The negative electrode sheet 2 precursor is subjected to high temperature treatment to obtain the negative electrode sheet 2 , so that the CMC in the negative electrode active material layer 22 is carbonized to form conductive carbon black.

[0058] When the single surface density of the positive electrode active material layer 12 is 200 g / m 2 As mentioned above, the system dynamics have deteriorated significantly, and the charging and discharging capabilities of the system need to be greatly improved.

[0059] Specifically, the present invention introduces a vacuum baking process into the negative electrode active material of the negative electrode, vacuum bakes the CMC in the negative electrode, and the CMC is treated at high temperature and carbonized into conductive carbon black to enhance the conductive network. At the same time, the CMC in the carbonized area on the surface of the pole piece will form a large number of micropores, which can effectively store electrolyte, improve low-temperature charging and discharging capabilities, and avoid lithium precipitation. However, the disadvantage is that after the pole piece is baked at high temperature in a vacuum, the pole piece will thicken, and when winding, the width of the winding core will increase, and the battery cell is prone to broken corners. Therefore, the baking time should not be too long, and should be controlled within 5 hours. If the baking time is too long, the pole piece will thicken and break.

[0060] like Figure 1-Figure 2 As shown, in one embodiment, the temperature of the high temperature treatment of the precursor of the negative electrode sheet 2 is 200° C. to 300° C., and the time of the high temperature treatment of the precursor of the negative electrode sheet 2 is 3-7 hours.

[0061] Specifically, the temperature of the high-temperature treatment of the precursor of the negative electrode sheet 2 is any point value among 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C or 300°C, or a range value consisting of any two point values; in a preferred embodiment, the temperature of the high-temperature treatment of the precursor of the negative electrode sheet 2 is 22°C~280°C.

[0062] Specifically, the time for high-temperature treatment of the precursor of the negative electrode sheet 2 is any point value among 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h or 7h, or a range value consisting of any two point values; in a preferred embodiment, the time for high-temperature treatment of the precursor of the negative electrode sheet 2 is 4-6h.

[0063] Specifically, when the temperature of the high-temperature treatment of the negative electrode sheet 2 precursor is 200°C~300°C, and the time of the high-temperature treatment of the negative electrode sheet 2 precursor is 3-7h, the CMC is carbonized into conductive carbon black after high-temperature treatment, thereby improving the conductive network. At the same time, the CMC in the carbonized area on the surface of the electrode sheet will form a large number of micropores, which can effectively store electrolyte, improve low-temperature charging and discharging capabilities, and avoid lithium precipitation.

[0064] When the temperature of the high-temperature treatment of the negative electrode sheet 2 precursor is lower than 200°C, CMC cannot be carbonized into conductive carbon black. When the temperature of the high-temperature treatment of the negative electrode sheet 2 precursor is higher than 300°C, it will cause partial loss of active materials, resulting in low capacity. At the same time, the baking temperature is too high, the electrode sheet is easy to expand, and the electrode sheet thickens, resulting in an increase in winding width, causing the battery cell to break after cycling. When the high-temperature treatment time of the negative electrode sheet 2 precursor is less than 3h, it will lead to poor baking effect, and the electrode sheet will not have a significant effect on improving kinetics. When the high-temperature treatment time of the negative electrode sheet 2 precursor is more than 7h, it will cause excessive loss of negative electrode surface density and a significant decrease in capacity. At the same time, the thickness of the negative electrode sheet will increase for a long time, resulting in the effect of battery cell cycle breaking. At the same time, the electrode sheet will crack, and the capacity retention rate will drop rapidly. High-temperature treatment temperature, the best choice is 350℃ 5h like Figure 1-Figure 2 As shown, in one embodiment, the negative electrode active material includes a silicon-carbon material, wherein the silicon content accounts for 3-15% of the mass of the silicon-carbon material.

[0065] Specifically, the silicon content accounts for any point value of 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% of the mass of the silicon-carbon material, or a range of values ​​consisting of any two point values; in a preferred embodiment, the silicon content accounts for 5%-10% of the mass of the silicon-carbon material.

[0066] When the silicon content accounts for 3-15% of the mass of the silicon-carbon material, it has the effects of high capacity, long cycle, low expansion, and no lithium deposition in the negative electrode arc; when the silicon content is less than 3% of the mass of the silicon-carbon material, the improvement effect is not obvious, because the kinetics of low silicon doping is close to that of the graphite system and the kinetics is excellent, and the addition of new processes has no obvious effect on its performance improvement; when the silicon content is greater than 15% of the mass of the silicon-carbon material, it has large cycle expansion, the battery cell is prone to failure over a long period of time, and lithium deposition in the negative electrode arc is obvious, and the performance deteriorates significantly and is not easy to improve.

[0067] A second aspect of the present invention provides a method for preparing an electrode assembly 100, comprising the following steps: S1. Obtain a positive electrode sheet 1, a negative electrode sheet 2 and a separator 3; S2. Etching a plurality of etching lines 1211 in the first region 121 of the positive electrode active material layer 12 of the positive electrode sheet 1, and pressing and embossing 1221 in the second region 122 of the positive electrode active material layer 12 of the positive electrode sheet 1; S3. The positive electrode sheet 1 , the separator 3 and the negative electrode sheet 2 are stacked and wound in sequence to form the electrode assembly 100 ; the first region 121 is located at the inner winding circle of the positive electrode sheet 1 , and the second region 122 is located at the outer winding circle of the positive electrode sheet 1 .

[0068] Specifically, in step S1 , the positive electrode sheet 1 includes a positive electrode current collector 11 and a positive electrode active material layer 12 coated on at least one side of the surface of the positive electrode current collector 11 , and the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder.

[0069] In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide (N x M y C z , x+y+z=1), nickel-cobalt-aluminum ternary material (NCA), lithium iron manganese phosphate (LiFe x Mn y PO4, x+y=1), lithium iron phosphate (LiFePO4), lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese-rich, lithium nickel manganese oxide (LMNO), lithium vanadium phosphate (Li3V2(PO4)3, LiVOPO4) or more.

[0070] In some embodiments, the positive electrode conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powders, metal fibers, and polyphenylene derivatives.

[0071] In some embodiments, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0072] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 95-99 wt % of positive electrode active material, 0.3-1.4 wt % of conductive agent, and 0.8-1.4 wt % of binder.

[0073] When the mass ratio of the positive electrode active material in the positive electrode active material layer is within the above range, the positive electrode sheet can have a higher lithium removal and lithium insertion capacity, and the battery can have a higher capacity.

[0074] The positive electrode current collector 11 is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector 11 includes one or more of nickel, tin, copper, and carbon materials. In a more preferred embodiment, the positive electrode current collector 11 is selected from aluminum foil.

[0075] The positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material layer is usually prepared by coating a positive electrode slurry made of a positive electrode active material, a positive electrode conductive agent, a positive electrode binder and any other components on a positive electrode current collector 11, followed by drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0076] In some embodiments, the negative electrode sheet 2 includes a negative electrode current collector 21 and a negative electrode active material layer coated on one or both sides of the negative electrode current collector 21 , wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0077] In one embodiment, the negative electrode active material includes metallic lithium, metallic lithium alloy, etc., a lithium-free negative electrode, etc.

[0078] In some embodiments, the negative electrode conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powders, metal fibers, and polyphenylene derivatives.

[0079] In some embodiments, the negative electrode binder includes one or more of CMC, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and polymethacrylic acid.

[0080] In some embodiments, the mass percentage of each component in the negative electrode active material layer is: 96%-97% of the negative electrode active material, 0.05%-0.5% of the conductive agent, and 1.5%-3.5% of the binder.

[0081] The negative electrode current collector 21 is selected from metal materials that can conduct electrons. Preferably, the negative electrode current collector 21 includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector 21 is selected from copper foil.

[0082] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material layer is usually prepared by coating a negative electrode slurry made of a negative electrode active material, a negative electrode conductive agent, a negative electrode binder and any other components on a negative electrode current collector 21, and then subjected to high temperature treatment to obtain a negative electrode sheet 2. The solvent can be an aqueous solvent, but is not limited thereto.

[0083] In some embodiments, the diaphragm 3 includes a base film and a coating layer. The base film adopts a porous PP layer to reduce the probability of pore blockage caused by high silicon side reactions. It has strong viscosity and the electrode is firmly adhered. The coating layer adopts an oily diaphragm coating layer. At the same time, a ceramic layer is added to the coating layer to enhance the liquid retention performance and safety performance and improve long-cycle circulation.

[0084] A third aspect of the present invention provides a battery, comprising a battery housing, an electrolyte, and the electrode assembly 100 as described above, or an electrode assembly 100 prepared by the method for preparing the electrode assembly 100 as described above.

[0085] In one embodiment, the electrolyte includes a lithium salt, a solvent and an additive; In some embodiments, the lithium salt can be selected from lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsF6, other organic lithium salts (such as lithium trifluoromethylsulfonate LiCF3SO, bis(trifluoromethylsulfonyl)imide lithium LiTFSI, bis(trifluoromethylsulfonyl)imide LiFSI, trifluoromethylsulfonyl-perfluorobutylsulfonylimide lithium LiTNFSI, fluorosulfonyl-perfluorobutylsulfonylimide lithium LiFNFSI, lithium bis(oxalatoborate) LiBOB, LiN(CF3SO2)2, LiC(SO2CF3)3) one or more; Lithium salt is Li in the electrolyte + Lithium salts are the source of ions, providing the battery with free-moving ions and playing the role of transporting ions inside the battery. In addition, lithium salts can also form a protective layer on the surface of electrode materials, which has an important influence on the battery's capacity, cycle performance, power density, energy density and other properties.

[0086] In some embodiments, the solvent can be selected from one or more of ethylene carbonate EC, propylene carbonate PC, butylene carbonate BC, dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, and -butyrolactone BL; the ether compound includes one or more of tetrahydrofuran THF, 2-methyl-tetrahydrofuran 2-Me-THF, dimethoxydimethyl ether DMM, and 1,2-dimethoxyethane DME.

[0087] In some embodiments, the additives may include film-forming additives, conductive additives, flame retardant additives, overcharge protection additives, additives for controlling the water and HF content in the electrolyte, general additives for improving low-temperature performance, or additives for improving the interface stability between the electrode and the electrolyte, such as fluoroethylene carbonate FEC.

[0088] In a preferred embodiment, the production of the battery includes the following steps: The electrode assembly 100 is placed in a battery shell formed by punching, and the electrolyte prepared as above is injected into the electrode assembly 100. After vacuum packaging, standing, forming and other processes, a metal battery is obtained.

[0089] The beneficial effects of the present invention are further illustrated below in conjunction with embodiments.

[0090] In order to make the invention purpose, technical scheme and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with examples. However, it should be understood that the examples of the present invention are only for explaining the present invention, not for limiting the present invention, and the examples of the present invention are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are made under conventional conditions, or are made under the conditions recommended by the material supplier.

[0091] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0092] In the following examples, the reagents, materials and instruments used, unless otherwise specified, can be purchased commercially or obtained by synthetic methods known in the art.

[0093] Table 1 Design of electrode assemblies of Examples 1-11 and Comparative Examples 1-6; Example 1 This embodiment is used to illustrate the electrode assembly and battery disclosed in the present invention; it includes the following operating steps: Production of positive electrode: The positive electrode active material lithium cobalt oxide, the conductive agent CNT, the conductive agent SP, and the adhesive PVDF are mixed in a mass ratio of 98.2:0.3:0.6:0.9. The mixture is fully stirred and mixed in NMP solvent to form a uniform positive electrode slurry. The viscosity of the positive electrode slurry meets 3500-5500mPas; the slurry is coated on at least one side of the positive electrode current collector aluminum foil, and after drying, rolling, die-cutting and other processes, a positive electrode sheet that meets the requirements is obtained.

[0094] The single surface density of the positive active material layer of the positive electrode sheet is 120 g / m 2; The number of windings in the first area is 1 / 4 of the total number of windings of the positive electrode sheet; multiple etching lines are etched in the first area, and the sum of the volumes of the etching areas of all etching lines is 1.2% of the volume of the positive electrode active material layer; the depth of the etching line is 30% of the thickness of the positive electrode active material layer; the spacing between two adjacent etching lines is 1.5mm; the width of the etching line is 75μm; the number of windings in the second area is 3 / 4 of the total number of windings of the positive electrode sheet; the second area is pressed and embossed, and the sum of the volumes of all embossed areas is 1.5% of the volume of the positive electrode active material layer; the embossed area accounts for 10% of the area of ​​the second area; the embossed depth is 2% of the thickness of the positive electrode active material layer; Negative electrode production: The negative electrode active material graphite, the negative electrode active material silicon carbon negative electrode, the conductive agent CNT, the conductive agent SP, the adhesive PAA, the adhesive SBR, and the adhesive CMC-Li are mixed in a mass ratio of 87.5:8.7:0.1:0.2:1.7:1.3:0.9. The mixture is fully stirred and mixed in a deionized water solvent to form a uniform negative electrode slurry. The slurry is applied to at least one side of the negative electrode current collector copper foil and baked at 300°C for 5 hours to obtain a negative electrode sheet.

[0095] Diaphragm production: The invention comprises a base film and a coating layer. A porous PP layer is used as the base film, and an oily diaphragm coating layer and a ceramic layer are arranged on the surface of the base film.

[0096] Preparation of electrolyte: The electrolyte includes lithium salt, solvent and additive; the lithium salt can be selected from lithium hexafluorophosphate LiPF6, the solvent is carbonate and carboxylate, and the additive is a film-forming additive, vinylene carbonate (VC), acrylonitrile, fluoroethylene carbonate (FEC).

[0097] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is located between the positive and negative electrodes to play a role of isolation, and then the positive electrode sheet, the separator and one end of the negative electrode sheet are wound to form an electrode assembly; so that the first area is located at the inner winding circle of the positive electrode sheet, and the second area is located at the outer winding circle of the positive electrode sheet; Then the rolled electrode assembly is placed in a battery housing, and the electrolyte prepared above is injected into the baked and dried battery cells, and a battery is obtained through vacuum packaging, standing, formation and other processes.

[0098] Example 2-11 Examples 2-11 are used to illustrate the electrode assembly disclosed in the present invention, and include most of the operating steps in Example 1, except that: Various components, parameters and contents of the electrode assembly shown in Table 1 were used.

[0099] Comparative Examples 1-6 Comparative Examples 1-6 are used to illustrate the electrode assembly disclosed in the present invention, including most of the operating steps in Example 1, except that: Various components, parameters and contents of the electrode assembly shown in Table 1 were used. Performance Testing The following performance tests were performed on the batteries prepared in the above Examples 1-11 and Comparative Examples 1-6: 1. Test of magnification capability: Tested at 25±2℃, discharged at 0.2C to 3.0V, left to stand for 10min Fully charged at 0.8C to 4.53V, cut-off current 0.05C, let stand for 10 minutes Discharge at 0.2C to 3V, let stand for 10min, and record the corresponding initial capacity C0 Fully charged at 0.8C, cut-off current 0.05C, let stand for 10 minutes Discharge at 0.5C to 3V, let stand for 10 minutes, and record the corresponding capacity C1. The 0.5C discharge capacity is C1 / C0.

[0100] (II) Battery initial performance test: initial discharge capacity / initial charge capacity (III) Battery low temperature discharge test: (1) Tested at 25±2℃, discharged at 0.2C to 3.0V, and left to stand for 10 minutes (2) Fully charged at 0.8C to 4.53V, cut-off current 0.05C, let stand for 10 minutes (3) Discharge at 0.2C to 3V, let stand for 10 minutes, and record the corresponding initial capacity C0 (4) Fully charged at 0.8C at 25°C, 4.53V, cut-off current 0.05C (5) Leave at 0℃ for 3 hours, then discharge at 0.2C to 3V, and record the discharge capacity C2 (6) Discharge C2 / C0 at 0℃.

[0101] (IV) Battery high temperature cycle test (1): At room temperature, record the initial voltage, thickness, and internal resistance (2): Stand at 45℃ for 2 hours (3): 0.5C constant current and constant voltage to 4.53V, cut-off current 0.05C, stand for 10 minutes (4): 0.5C discharge to 3V, let stand for 10 minutes (5): Repeat steps 3 and 4 500 times and record the discharge data as well as the 50 / 100 / 200 / 300 / 400 / 500 cycle voltage, internal resistance, and thickness.

[0102] The test results are shown in Table 2.

[0103] Table 2 Battery electrochemical performance It can be seen from Table 1 and Table 2 that, by comparing Examples 1-11 with Comparative Examples 1-2, when the number of winding folds in the first area is 1 / 4-1 / 2 of the total number of winding folds of the positive electrode sheet, or when the sum of the volumes of the etched areas of all etched lines is 1%-2% of the volume of the positive electrode active material layer, or when the depth of the etched line is 25%-40% of the thickness of the positive electrode active material layer, or when the spacing between two adjacent etched lines is 0.5mm-1.5mm, or when the width of the etched line is 60μm-105μm, or when the sum of the volumes of all embossed areas is 1.5%-7% of the volume of the positive electrode active material layer, or when the embossed area accounts for 10%-50% of the area of ​​the second area, or when the embossing depth is 2%-10% of the thickness of the positive electrode active material layer, the high capacity of the core can be maintained while taking into account the long cycle performance of the core, and the problem of lithium plating in the arc area of ​​the positive electrode sheet can be effectively improved.

[0104] When at least one of the above conditions is not met, the N / P value of the inner winding core will change less, and the improvement of the negative arc area corresponding to the positive electrode sheet will not be obvious, and the capacity will be lost at the same time; or the CB value of the negative arc area corresponding to the positive electrode sheet will be too large, resulting in a large loss of core capacity and deterioration of high-temperature cycle retention rate.

[0105] By comparing Examples 1-11 with Comparative Examples 3-6, it can be seen that when the temperature of the high-temperature treatment of the negative electrode precursor is 200°C~300°C and the time of the high-temperature treatment of the negative electrode precursor is 3-7h, the CMC is carbonized into conductive carbon black after high-temperature treatment, thereby improving the conductive network. At the same time, the CMC in the carbonized area on the surface of the electrode will form a large number of micropores, which can effectively store electrolyte, improve low-temperature charging and discharging capabilities, and avoid lithium precipitation.

[0106] When the temperature of the high-temperature treatment of the negative electrode precursor is lower than 200°C, CMC cannot be carbonized into conductive carbon black. When the temperature of the high-temperature treatment of the negative electrode precursor is higher than 300°C, it will cause some active material loss, resulting in low capacity. At the same time, if the baking temperature is too high, the electrode sheet is easy to expand, and the electrode sheet will increase in thickness, resulting in an increase in the winding width, which will cause the battery cell to break after the cycle.

[0107] When the high-temperature treatment time of the negative electrode precursor is less than 3h, the baking effect will be poor, and the electrode will not have obvious effect on the kinetic improvement; when the high-temperature treatment time of the negative electrode precursor is greater than 7h, it will lead to excessive loss of negative electrode surface density and a significant decrease in capacity. At the same time, the thickness of the negative electrode will increase for a long time, and the battery cell will break during cycle. At the same time, the electrode will crack and the capacity retention rate will drop rapidly.

[0108] 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 in the protection scope of the present invention.

Claims

1. An electrode assembly, characterized in that: It includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form the electrode assembly; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on at least one side of the surface of the positive electrode current collector, and the single surface density of the positive electrode active material layer is 120 g / m 2 ~300g / m 2 ; The positive electrode active material layer includes a first region and a second region, the first region is located in the inner winding circle of the positive electrode sheet, and the second region is located in the outer winding circle of the positive electrode sheet; along a direction parallel to the thickness of the positive electrode sheet, the first region of the positive electrode active material layer is provided with multiple etching lines; the second region of the positive electrode sheet is provided with multiple embossings.

2. The electrode assembly according to claim 1, characterized in that: The number of winding folds of the first region is 1 / 4-1 / 2 of the total number of winding folds of the positive electrode sheet.

3. The electrode assembly according to claim 1, characterized in that: The total volume of the etched areas of all the etched lines is 1%-2% of the volume of the positive electrode active material layer.

4. The electrode assembly according to claim 3, characterized in that: The depth of the etching line is 25% to 40% of the thickness of the positive electrode active material layer; the spacing between two adjacent etching lines is 0.5 mm to 1.5 mm; and the width of the etching line is 60 μm to 105 μm.

5. The electrode assembly according to claim 4, characterized in that: The depth of the etching line is 30% to 35% of the thickness of the positive electrode active material layer; the spacing between two adjacent etching lines is 0.8 mm to 1.2 mm; and the width of the etching line is 75 μm to 90 μm.

6. The electrode assembly according to claim 1, characterized in that: The number of winding folds of the second region is 1 / 2-3 / 4 of the total number of winding folds of the positive electrode sheet.

7. The electrode assembly according to claim 1, characterized in that: The total volume of all the embossed areas is 1.5% to 7% of the volume of the positive electrode active material layer.

8. The electrode assembly according to claim 1, characterized in that: The embossing area accounts for 10% to 50% of the area of ​​the second region.

9. The electrode assembly according to claim 1, characterized in that: Along a direction parallel to the thickness of the positive electrode sheet, the depth of the embossing is 2%-10% of the thickness of the positive electrode active material layer.

10. The electrode assembly according to claim 1, characterized in that: The single surface density of the positive electrode active material layer is 200 g / m 2 ~300g / m 2 ; The negative electrode sheet precursor comprises a negative electrode current collector and a negative electrode active material layer coated on at least one side of the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material and CMC; The negative electrode sheet precursor is subjected to high temperature treatment to obtain the negative electrode sheet, so that the CMC in the negative electrode active material layer is carbonized to form conductive carbon black.

11. The electrode assembly according to claim 10, characterized in that: The temperature of the high temperature treatment of the negative electrode sheet precursor is 200° C. to 300° C., and the time of the high temperature treatment of the negative electrode sheet precursor is 3-7 hours.

12. The electrode assembly according to claim 10, characterized in that: The negative electrode active material comprises a silicon-carbon material, wherein the silicon content accounts for 3-15% of the mass of the silicon-carbon material.

13. The method for preparing an electrode assembly according to any one of claims 1 to 11, characterized in that: The following steps are involved: S1. Obtain a positive electrode sheet, a negative electrode sheet and a separator; S2. etching a plurality of etching lines in a first region of the positive electrode active material layer of the positive electrode sheet, and embossing in a second region of the positive electrode active material layer of the positive electrode sheet; S3. Stack and wind the positive electrode sheet, the separator and the negative electrode sheet in sequence to form an electrode assembly; so that the first region is located in the inner winding circle of the positive electrode sheet, and the second region is located in the outer winding circle of the positive electrode sheet.

14. A battery, characterized in that: It comprises a battery shell, an electrolyte and an electrode assembly as described in any one of claims 1 to 12, or an electrode assembly prepared by the preparation method of the electrode assembly as described in claim 13.

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