An electrode assembly and a battery using the same

Abstract

This invention provides an electrode assembly and a battery using the same. The electrode assembly includes a positive electrode, a separator, and a negative electrode stacked together; the positive electrode, separator, and negative electrode are wound along the y-direction; the positive electrode includes a stacked positive active material layer and a positive current collector, the positive active material layer including a corner region and a large surface region; the corner region is a corner region formed by the winding of the positive active material layer along the y-direction, and contains a phosphate positive active material; the large surface region is a planar region connecting two adjacent corner regions in the y-direction, and contains both phosphate positive active materials and ternary positive active materials. The electrode assembly provided by this invention can fully utilize the advantages of high safety and long cycle life of phosphate positive active materials, as well as the advantages of high ionic conductivity and high energy density of ternary positive active materials.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an electrode assembly and a battery using the same. Background Technology

[0002] In lithium-ion battery technology, phosphate cathode materials are known for their excellent safety and cycle life, but their energy density and ionic conductivity are typically low. Ternary cathode materials, on the other hand, possess higher ionic conductivity and energy density, but there is room for improvement in their cycle life and thermal stability. Therefore, the industry is attempting to combine the two to improve energy density while maintaining battery safety and cycle performance.

[0003] Currently, common composite cathode fabrication processes often involve coating a mixture of phosphate and ternary materials onto a current collector. However, due to the differences in physical properties between the two materials, achieving uniform dispersion when directly mixing them in a slurry is difficult. This results in electrodes produced using this process often exhibiting poor uniformity of the active coating. Batteries made using this method frequently show high internal resistance during cycling, leading to insufficient cycle stability and electrochemical performance. Furthermore, it fails to fully leverage the performance advantages of both phosphate and ternary cathode materials. Additionally, the overall safety performance of these batteries requires further improvement. Summary of the Invention

[0004] The present invention provides an electrode assembly and a battery using the same, so that the electrode assembly can maintain good energy density while improving its safety performance and cycle life.

[0005] According to a first aspect of the present invention, an electrode assembly is provided, comprising a positive electrode sheet, a separator, and a negative electrode sheet stacked together; the positive electrode sheet, the separator, and the negative electrode sheet are wound along the y-direction; the positive electrode sheet includes a positive active material layer and a positive current collector stacked together, the positive active material layer including an R-corner region and a large surface region; the R-corner region is a corner region formed by the winding of the positive active material layer along the y-direction, and the positive active material contained therein is a phosphate positive active material; the large surface region is a planar region connecting two adjacent R-corner regions in the y-direction, and the positive active material contained therein includes a phosphate positive active material and a ternary positive active material.

[0006] In the electrode assembly provided by this invention, only phosphate cathode active material is used in the R-corner region of the positive electrode, while both phosphate and ternary cathode active materials are used in the larger area of ​​the positive electrode. This design allows the R-corner region to have a higher local N / P ratio compared to the larger area, as it uses only phosphate material with relatively low specific capacity. This effectively suppresses lithium plating tendency at the R-corner during cycling, improving the cycle stability and safety of the cell. Simultaneously, since no ternary material is used in the R-corner region, the continuous thermal propagation path of the ternary material along the winding direction is physically blocked, significantly reducing the risk of thermal runaway. Based on the above-mentioned partitioning arrangement of the positive electrode, the electrode assembly provided by this invention can fully utilize the advantages of high safety and long cycle life of phosphate cathode active material, as well as the advantages of high ionic conductivity and high energy density of ternary cathode active material. This allows the electrode assembly to achieve a synergistic improvement in safety performance and cycle life while maintaining energy density.

[0007] In the electrode assembly provided by this invention, the spacing between the R-angle regions of the positive electrode sheet is a fixed value, which is 1 / 2 of the circumference of the winding needle. The formula for calculating the R-angle length along the length direction of the positive electrode sheet is as follows: Calculation of the length of the first R-angle (the first corner formed by the positive electrode sheet from the winding axis): L1=π*(CT+AT+(n+1)*ST) Other radius (R) length calculations: ① The length of the odd-numbered R-angles (intervals of an even number of R-angle regions with the first R-angle region): L 奇 =π*(N*(CT+AT+2*ST)+(n-1)*ST) ② The length of the even-numbered R-angle (interval with an odd number of R-angle regions to the first R-angle region): L 偶 =π*((N-1)*(CT+AT+2*ST)+ST) Where N is the number of winding turns at the R-angle of the electrode assembly (N≥2), n is the number of empty layers of the feed separator, CT is the thickness of the positive electrode, AT is the thickness of the negative electrode, and ST is the thickness of the separator. The "number of empty layers of feed separator" refers to the number of layers of separator that are initially wound empty (only separator, no electrode) after the start of the winding process. After these empty turns, the separator is wound together with the positive and negative electrode sheets to form the battery cell.

[0008] Furthermore, the large area includes several ternary cathode active material regions and several phosphate cathode active material regions. The cathode active material regions contain ternary cathode active materials, and the cathode active material regions contain phosphate cathode active materials. The large area includes a first cathode active material layer and a second cathode active material layer stacked along the z-direction, with the z-direction perpendicular to the large area. Both the first and second cathode active material layers independently include several ternary cathode active material regions and several phosphate cathode active material regions. The first and second cathode active material layers are staggered in the z-direction, such that in the z-direction, at least a partial projection of any ternary cathode active material region overlaps with a phosphate cathode active material region. By stacking first and second positive electrode active material layers over a large area of ​​the positive electrode sheet and staggering them in the thickness direction (z-direction), the ternary positive electrode active material regions and phosphate positive electrode active material regions located in different layers form an overlapping projection relationship in the thickness direction. This structural design can utilize the relatively good thermal stability of phosphate materials to form a local thermal buffer interface in the thickness direction of the positive electrode sheet. This helps to mitigate the heat transfer along the thickness direction that may be generated by the ternary material under cycling or abnormal conditions, thus providing favorable conditions for improving the cycle stability and thermal safety of the battery cell.

[0009] Furthermore, in the large area, phosphate cathode active material regions are provided between any adjacent ternary cathode active material regions to form an isolation. By providing phosphate cathode active material regions for isolation between any adjacent ternary cathode active material regions in the large area, and combining these phosphate cathode active material regions with the aforementioned staggered arrangement in the thickness direction, a three-dimensional separation of the ternary cathode active material regions can be formed. Based on the relatively good thermal stability of phosphate materials, this separation structure helps to suppress heat transfer between the ternary cathode active material regions from multiple directions, thereby providing further structural support for mitigating heat spread and improving the safety performance of the battery cell.

[0010] Furthermore, on the composite surface of the first and second positive electrode active material layers, the distance between any two adjacent ternary positive electrode active material regions belonging to different layers in the width direction of the large area is d, where 0 mm < d ≤ 2 mm. By controlling the value of d within the above range: on the one hand, by setting 0 < d, it is ensured that the two ternary positive electrode active material regions belonging to the first and second positive electrode active material layers form a barrier on the composite surface of the first and second positive electrode active material layers, thereby blocking the heat transfer from the ternary positive electrode active material regions along the z-direction of the positive electrode 9 sheets with the help of the intermediate phosphate active material region; on the other hand, by setting d ≤ 2 mm, it helps to reduce the non-uniformity of lithium intercalation caused by the capacity difference between the phosphate positive electrode active material region and the adjacent region, thereby improving thermal safety and promoting the uniform intercalation of lithium ions during cycling, thus improving the cycle stability of the cell.

[0011] Furthermore, based on mass percentage, the content of ternary cathode active material in the ternary cathode active material region is 93%–95%, and the content of phosphate cathode active material in the phosphate cathode active material region is 88%–93%.

[0012] Furthermore, the compaction density of the ternary cathode active material region is P1, and that of the phosphate cathode active material region is P2, where P2 < P1. Controlling P2 < P1 helps to increase the porosity of the phosphate cathode active material region, thereby improving its internal ion transport efficiency. This design helps to reduce the difference in ion transport efficiency between the phosphate cathode active material region and the ternary cathode active material region, reducing the ion migration resistance at the interface between regions containing different cathode active materials, and thus improving the overall lithium-ion conductivity of the cathode active material layer, enabling the cell to achieve superior rate performance.

[0013] Furthermore, the ternary cathode active material region and the phosphate cathode active material region satisfy P1 / P2 = 1.2 to 1.5.

[0014] Furthermore, the mass fraction of the conductive agent in the phosphate cathode active material region is higher than that in the ternary cathode active material region. By having a higher mass fraction of conductive agent in the phosphate cathode active material region, the electronic conductivity of this region is effectively improved. This design helps to balance the difference in conductivity between the phosphate cathode active material region and the ternary cathode active material region, reduces the contact resistance at the interface between regions containing different cathode active materials, thereby improving the overall electronic conduction efficiency of the cathode active material layer and enabling the cell to exhibit superior rate performance.

[0015] Furthermore, the mass fraction of the conductive agent in the phosphate cathode active material region is 4.9% to 10%, and the mass fraction of the conductive agent in the ternary cathode active material region is 2.9% to 4.1%.

[0016] Furthermore, the positive electrode active material layer contains phosphate positive electrode active materials, including carbon-coated phosphate positive electrode active materials. Using carbon-coated phosphate positive electrode active materials can improve the conductivity of the phosphate positive electrode active material region. This design helps to balance the conductivity difference between the phosphate positive electrode active material region and the ternary positive electrode active material region, reduces the contact resistance at the interface between regions containing different positive electrode active materials, and further improves the overall electronic conduction efficiency of the positive electrode active material layer, enabling the cell to exhibit superior rate performance.

[0017] Furthermore, the thickness of the first positive electrode active material layer is 20–50 μm, and the thickness of the second positive electrode active material layer is 20–50 μm.

[0018] Furthermore, on the plane formed by the width direction and the z-direction of the large area, the cross-sectional shape of the ternary cathode active material region and the phosphate cathode active material region is at least one of parallelogram, rectangle, trapezoid or irregular quadrilateral, and the cross-sectional shapes of the ternary cathode active material region and the phosphate cathode active material region are the same or different.

[0019] According to a second aspect of the present invention, a battery is provided, comprising the electrode assembly as described above. The battery provided by the present invention synergistically leverages the high safety of phosphate materials and the high energy density of ternary materials, thereby improving overall cycle life and safety performance while maintaining high energy density. Attached Figure Description

[0020] Figure 1 This is a top view of the positive electrode sheet prepared in Example 1 in its spread-out state; Figure 2 This is a schematic cross-sectional view of the positive electrode sheet prepared in Example 1 on the plane defined by the width direction and the z-direction of the large area region. Figure 3 This is a schematic cross-sectional view of the positive electrode sheet prepared in Example 1 on the plane defined by the width direction and the z direction of the R-angle region; Figure 4 This is a schematic cross-sectional view of the positive electrode sheet prepared in Example 3 on the plane defined by the width direction and the z-direction of the large area region. Figure 5 This is a schematic cross-sectional view of the positive electrode sheet prepared in Example 12 on the plane defined by the width direction and the z-direction of the large area region. Figure 6 This is a schematic cross-sectional view of the positive electrode sheet prepared in Example 13 on the plane defined by the width direction and the z-direction of the large area region. Figure 7 This is a schematic cross-sectional view of the positive electrode sheet prepared in Example 14 on the plane defined by the width direction and the z-direction of the large area region.

[0021] In the above figures, the corresponding relationships of the reference numerals are as follows: 1. First positive electrode active material layer, 2. Second positive electrode active material layer, 3. Ternary positive electrode active material region, 4. Phosphate positive electrode active region, 5. Current collector.

[0022] In the above figures, the specific meanings of the directions are as follows: the x-direction indicates the width direction of the large area of ​​the positive electrode plate, the y-direction indicates the length direction of the large area of ​​the positive electrode plate, and the z-direction indicates the direction perpendicular to the large area of ​​the positive electrode plate. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] Example 1 This embodiment provides a method for preparing a lithium-ion battery, the specific steps of which are as follows: 1. Fabrication of electrode components (1) Preparation of the positive electrode: S1. Prepare phosphate slurry and ternary slurry separately. The phosphate slurry uses lithium iron phosphate as the phosphate positive electrode active material, with a composition of lithium iron phosphate: conductive agent: binder = 88:8:4 by mass, and a solid content of 70wt%. The ternary slurry uses NCM622 as the ternary positive electrode active material, with a composition of NCM622: conductive agent: binder = 93:3:4 by mass, and a solid content of 74wt%.

[0025] S2. Perform the first layer coating and drying. The above-mentioned ternary slurry and phosphate slurry are coated alternately along the width direction of the flat current collector 5 to form a first positive electrode active material layer 1 over a large area. This layer includes materials along the width direction of the large area (…). Figure 1 The ternary cathode active material region 3 and the phosphate cathode active material region 4 are arranged alternately in a cuboid shape (as shown in the x-direction). Figure 1 As shown, the ternary cathode active material region 3 and the phosphate cathode active material region 4 formed thus have rectangular cross-sectional shapes on the plane defined by the direction parallel to the width of the large surface region and the z-direction. Along the width of the large surface region, the width of the ternary cathode active material region 3 is L, and the width of the phosphate cathode active material region 4 is L' (L' > L). Simultaneously, according to the length direction of the cathode sheet (… Figure 1The corner region (R-corner region) formed by winding in the y-direction (as shown) is entirely coated with phosphate slurry in the width direction to form the phosphate positive electrode active material region 4 in the R-corner region. It is then dried to allow the solvent to evaporate and the coating to cure. The thickness of both the first positive electrode active material layer 1 and the phosphate positive electrode active material region 4 formed in the R-corner region in this step is controlled to be 25 μm.

[0026] S3. Perform the second coating and drying. Coat the first positive electrode active material layer 1 with ternary slurry and phosphate slurry to form the second positive electrode active material layer 2 covering a large area. Similar to the first positive electrode active material layer 1, the second positive electrode active material layer 2 is also composed of ternary positive electrode active material regions 3 and phosphate positive electrode active material regions 4 arranged alternately along the width direction of the large area in a cuboid shape. The ternary positive electrode active material region 3 and phosphate positive electrode active material region 4 formed therefrom have a rectangular cross-sectional shape on the plane determined by the plane parallel to the width direction of the large area and the z-direction. Along the width direction of the large area, the width of the ternary positive electrode active material region 3 is D, and the width of the phosphate positive electrode active material region 4 is L' (L'>L). During coating, the positions of each material region in the second positive electrode active material layer 2 are controlled so that they satisfy the following positional relationship with the material regions in the first positive electrode active material layer 1 that are directly opposite each other in the z-direction (perpendicular to the large surface area): On the composite plane formed by the first positive electrode active material layer 1 and the second positive electrode active material layer 2, the area occupied by the phosphate positive electrode active material region 4 in the first positive electrode active material layer 1 is completely covered and larger than the area occupied by the ternary positive electrode active material region 3 directly opposite it in the second positive electrode active material layer 2. Simultaneously, the area occupied by the phosphate positive electrode active material region 4 in the second positive electrode active material layer 2 is also completely covered and larger than the area occupied by the ternary positive electrode active material region 3 directly opposite it in the first positive electrode active material layer 1. In both of these cases, the edge distance between the mutually opposite phosphate positive electrode active material region 4 and the ternary positive electrode active material region 3 in the width direction of the large surface area is (L'-L) / 2, as shown above. Figure 2 As shown. Through the above coating control, the projections of the ternary positive electrode active material regions 3 belonging to the first positive electrode active material layer 1 and the second positive electrode active material layer 2 in the z-direction are alternately arranged in the width direction of the large area of ​​the positive electrode sheet. On the composite surface of the first positive electrode active material layer 1 and the second positive electrode active material layer 2, the spacing d = (L' - L) / 2 between any two adjacent ternary positive electrode active material regions 3 belonging to different layers in the width direction of the large area, where d is 2 mm. At the same time, according to the positive electrode sheet along the length direction ( Figure 1 The corner region (R-corner region) formed by winding in the y-direction (as shown) is entirely coated with phosphate slurry in the width direction to form the phosphate positive electrode active material region 4 of the R-corner region, as shown. Figure 3As shown. Drying is then performed to allow the solvent to evaporate and the coating to cure. The thickness of the second positive electrode active material layer 2 and the phosphate positive electrode active material region 4 formed in the R-corner region in this step are both controlled to 25 μm.

[0027] S4. The positive electrode sheet after the above coating and drying steps are cold-pressed. Process parameters: temperature 25℃, rolling pressure 3000kN / m, rolling speed 33m / min. After cold pressing, the compaction density P1 of the ternary positive electrode active material region 3 in the positive electrode sheet reaches 3.11g / cm³. 3 The compaction density P2 of region 4 of the phosphate positive electrode active material reaches 2.55 g / cm³. 3 The compaction density of the ternary cathode active material region and the phosphate cathode active material region can be controlled by adjusting the solid content of the ternary slurry and the phosphate slurry, as well as the rolling pressure and speed during the cold pressing process. In this embodiment, the ternary slurry and the phosphate slurry have different solid contents, so different compaction densities can be achieved in the ternary cathode active material region 3 and the phosphate cathode active material region 4 through a single cold pressing.

[0028] (2) Preparation of negative electrode A negative electrode slurry (formulation: graphite: conductive agent: binder = 96.2:1:2.8) was prepared, coated onto the current collector, and the N / P ratio was controlled at 1.1. After drying and rolling, a negative electrode sheet of 95 μm was obtained.

[0029] (3) Assembly of electrode assembly The positive electrode sheet, negative electrode sheet, and separator with a thickness of 16 μm and a ceramic coating prepared in this embodiment are sequentially stacked and wound along the y-direction to assemble a bare battery cell. The bare battery cell has 4 unwound separator layers and 30 winding turns.

[0030] 2. Encased in a housing The bare cells were installed into a battery casing, injected with 1.1 mol / L LiPF6 electrolyte (solvent ratio EC:EMC:DMC=3:4:3) and encapsulated to finally obtain a lithium-ion battery.

[0031] Example 2 This embodiment uses Example 1 as a reference to prepare a lithium-ion battery. The difference from Example 1 is: (1) In this embodiment, the composition of the slurry containing positive electrode active material is calculated according to the mass ratio. The composition of the ternary slurry is NCM622: conductive agent: binder = 95:3:2, and the composition of the phosphate slurry is lithium iron phosphate: conductive agent: binder = 90:8:2.

[0032] (2) In step S3 of the positive electrode preparation, by coating control, the spacing d between the adjacent ternary positive electrode active material regions belonging to the first positive electrode active material layer and the second positive electrode active material layer on the composite plane of the first positive electrode active material layer and the second positive electrode active material layer is 0 mm, that is, the two ternary regions are directly connected in the width direction.

[0033] (3) In steps S2 and S3, the thickness of the first positive electrode active material layer and the second positive electrode active material layer (including the corresponding R-corner region) are both controlled to be 35 μm.

[0034] (4) The cold pressing parameters for step S4 are: temperature 25℃, roller pressure 3600kN / m, roller speed 27m / min, and the compaction density P1 of the ternary cathode active material region after cold pressing is 3.32 g / cm³. 3 The compaction density P2 of the phosphate positive electrode active material region is 2.55 g / cm³. 3 Compared to Example 1, the compaction density of the ternary cathode active material region obtained in this example is increased. This is because the roller pressure is increased, resulting in more thorough compression of the ternary cathode active material region. Meanwhile, the compaction density of the phosphate cathode active material regions in both examples is basically the same. This is because the cold pressing roller speed in both examples is maintained at a high level. Therefore, during the cold pressing process, only the surface area of ​​the phosphate cathode active material region is slightly compacted, while there are still many voids inside. As a result, the overall compaction density of both examples is basically the same and lower than that of the ternary cathode active material region.

[0035] (5) The thickness of the negative electrode sheet after rolling is 129 μm.

[0036] Apart from the differences mentioned above, the materials and operating steps used in the preparation of the positive electrode sheet, as well as the materials and operating steps used in the subsequent preparation of the negative electrode sheet, assembly of the electrode assembly, and encapsulation process, are the same as those in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0037] Example 3 This embodiment uses Example 1 as a reference to prepare a lithium-ion battery. The difference from Example 1 is: (1) In this embodiment, the composition of the slurry containing positive electrode active material is calculated according to the mass ratio. The composition of the ternary slurry is NCM622: conductive agent: binder = 95:3:2; the composition of the phosphate slurry is lithium iron phosphate: conductive agent: binder = 90:8:2.

[0038] (2) In steps S2 and S3 of the positive electrode preparation, the ternary positive electrode active material region 3 and the phosphate positive electrode active material region 4 are parallel to the width direction of the large area region ( Figure 4The cross-sectional shapes on the planes defined by the x-direction and z-direction are the same, both being isosceles trapezoids. Along the width of the large area, the width of the long base of this isosceles trapezoid is W', and the width of the short base is W (W' > W). Figure 4 As shown. Within the same positive electrode active material layer (first positive electrode active material layer 1 or second positive electrode active material layer 2), ternary positive electrode active material regions 3 and phosphate positive electrode active material regions 4 are arranged alternately facing each other along the width direction. Specifically, the short bottom edge (W) of one ternary positive electrode active material region 3 is adjacent to the long bottom edge (W') of the adjacent phosphate positive electrode active material region 4, while the long bottom edge (W') of the ternary positive electrode active material region 3 is adjacent to the short bottom edge (W) of the phosphate positive electrode active material region 4 on the other side. Between the first positive electrode active material layer 1 and the second positive electrode active material layer 2, the coating control satisfies the following: the short bottom edge (W) of the ternary positive electrode active material region 3 located in the first positive electrode active material layer 1 (or the second positive electrode active material layer 2) is adjacent to the long bottom edge (W') of the phosphate positive electrode active material region 4 located in the second positive electrode active material layer 2 (or the first positive electrode active material layer 1) that is directly opposite it in the z-direction. This arrangement results in the ternary positive electrode active material regions 3 belonging to the first positive electrode active material layer 1 and the second positive electrode active material layer 2 being arranged alternately in opposite directions along the width of the composite plane of the first positive electrode active material layer 1 and the second positive electrode active material layer 2, and the minimum spacing between any two adjacent ternary positive electrode active material regions 3 belonging to different layers in the width direction is d = (W' - W) / 2 = 1 mm.

[0039] (3) In steps S2 and S3, the thickness of the first positive electrode active material layer 1 and the second positive electrode active material layer 2 (including the corresponding R-corner region) is controlled to be 35 μm. The cold pressing parameters for step S4 are: temperature 25℃, rolling pressure 3600kN / m, rolling speed 27m / min, and the compaction density P1 of the ternary positive electrode active material region 3 after cold pressing is 3.32 g / cm³. 3 The compaction density P2 of region 4 of the phosphate positive electrode active material is 2.55 g / cm³. 3 .

[0040] (4) The thickness of the negative electrode sheet after rolling is 129 μm.

[0041] Apart from the differences mentioned above, the materials and operating steps used in the preparation of the positive electrode sheet, as well as the materials and operating steps used in the subsequent preparation of the negative electrode sheet, assembly of the electrode assembly, and encapsulation process, are the same as those in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0042] Example 4 This embodiment refers to Example 1 to prepare a lithium-ion battery. The difference from Example 1 is that in this embodiment, when preparing the positive electrode sheet, only one layer of positive electrode active material with a thickness of 50 μm is set in its large area. This layer contains ternary positive electrode active material regions and phosphate positive electrode active material regions that are alternately arranged along the width direction of the current collector (the arrangement is the same as the first positive electrode active material layer formed in step S2 of Example 1) and are in the shape of cuboids. The cross-sectional shape of the ternary positive electrode active material region and the phosphate positive electrode active material region on the plane determined by the plane parallel to the width direction of the large area and the z-direction is rectangular. The ternary positive electrode active material region and the phosphate positive electrode active material region prepared in this embodiment have the same length and width as the active material region using the same positive electrode active material in Example 1.

[0043] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery are the same as in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0044] Example 5 This embodiment uses Example 1 as a reference to prepare a lithium-ion battery. The difference from Example 1 is: In step S3 of the positive electrode preparation, by coating control, the spacing d between adjacent ternary positive electrode active material regions belonging to the first positive electrode active material layer and the second positive electrode active material layer on the composite plane of the first positive electrode active material layer and the second positive electrode active material layer is 0 mm, that is, the two ternary regions are directly connected in the width direction.

[0045] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery are the same as in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0046] Example 6 This embodiment refers to Example 1 to prepare a lithium-ion battery. The difference from Example 1 is that in step S3 of the positive electrode preparation, by coating control, the spacing d between adjacent ternary positive electrode active material regions belonging to the first positive electrode active material layer and the second positive electrode active material layer on the composite plane of the first positive electrode active material layer and the second positive electrode active material layer is 2.5 mm.

[0047] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery are the same as in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0048] Example 7 This embodiment refers to Example 1 to prepare a lithium-ion battery. The difference from Example 1 is that in step S1 of the positive electrode preparation, the solid content of the phosphate slurry is 66 wt%, and the solid content of the ternary slurry is 76 wt%; in step S4 of the positive electrode preparation, the cold pressing parameters are: temperature 25℃, rolling pressure 4100 kN / m, rolling speed 20 m / min, and the compaction density P1 of the ternary positive electrode active material region after cold pressing is 3.55 g / cm³. 3 The compaction density P2 of the phosphate positive electrode active material region is 2.36 g / cm³. 3 .

[0049] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery are the same as in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0050] Example 8 This embodiment refers to Example 1 to prepare a lithium-ion battery. The difference from Example 1 is that in step S1 of the positive electrode preparation, the solid content of the phosphate slurry is 64 wt%, and the solid content of the ternary slurry is 76 wt%; in step S4 of the positive electrode preparation, the cold pressing parameters are: temperature 25℃, rolling pressure 4100 kN / m, rolling speed 20 m / min, and the compaction density P1 of the ternary positive electrode active material region after cold pressing is 3.55 g / cm³. 3 The compaction density P2 of the phosphate positive electrode active material region is 2.3 g / cm³. 3 .

[0051] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery are the same as in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0052] Example 9 This embodiment refers to Example 1 to prepare a lithium-ion battery. The difference from Example 1 is that in step S1 of the positive electrode preparation, the solid content of the phosphate slurry is 72 wt%, and the solid content of the ternary slurry is 72 wt%; in step S4 of the positive electrode preparation, the cold pressing parameters are: temperature 25℃, rolling pressure 3400 kN / m, rolling speed 30 m / min, and the compaction density P1 of the ternary positive electrode active material region after cold pressing is 3.1 g / cm³. 3 The compaction density P2 of the phosphate positive electrode active material region is 2.65 g / cm³. 3 .

[0053] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery are the same as in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0054] Example 10 This embodiment uses Example 1 as a reference to prepare a lithium-ion battery. The difference from Example 1 is: In this embodiment, the composition of the slurry containing positive electrode active material is calculated by mass ratio. The composition of the ternary slurry is NCM622: conductive agent: binder = 93:3:4, and the composition of the phosphate slurry is lithium iron phosphate: conductive agent: binder = 93:3:4.

[0055] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery are the same as in Example 1, thereby finally obtaining the lithium-ion battery of this example.

[0056] Example 11 This embodiment refers to Example 1 to prepare a lithium-ion battery. The difference from Example 1 is that the positive electrode active material used in this embodiment is carbon-coated lithium iron phosphate.

[0057] Apart from the differences mentioned above, the materials and their proportions, operating steps, and other materials used in the preparation of the positive electrode sheet in this embodiment are the same as those in Example 1, thereby finally obtaining the lithium-ion battery of this embodiment.

[0058] Comparative Example 1 This comparative example uses Example 1 as a reference to prepare a lithium-ion battery. The difference from Example 1 is that, in preparing the positive electrode sheet in this comparative example, the positive electrode active material contained in the R-corner region also includes ternary positive electrode active material and phosphate positive electrode active material, and the arrangement of the ternary positive electrode active material region and the phosphate positive electrode active material region in this region is the same as the arrangement of the large area region in Example 1. That is, the positive electrode active material layer in this region is also composed of alternating ternary material region and phosphate material region in the z-direction.

[0059] Apart from the differences mentioned above, the materials used in this comparative example, their proportions, operating steps, and other materials used in preparing the positive electrode sheet are the same as those in Example 1, thereby finally obtaining the lithium-ion battery of this comparative example.

[0060] Comparative Example 2 This comparative example uses Example 1 as a reference to prepare a lithium-ion battery. The difference from Example 1 is that the positive electrode active material layer in this comparative example is not partitioned or layered. Specifically, a ternary positive electrode active material (NCM622) and a phosphate positive electrode active material (lithium iron phosphate) are mixed and slurried. The resulting slurry has a mass ratio of NCM622:lithium iron phosphate:conductive agent:binder = 46.5:44:5.5:4. This slurry is then used to coat a single layer onto a flat current collector surface. The resulting positive electrode active material layer covers both the large surface area and the rounded corner area, with a thickness of 50 μm. After cold pressing, the compaction density of this positive electrode active material layer is 3.12 g / cm³. 3 Apart from the differences mentioned above, the materials used in this comparative example, their proportions, operating steps, and other materials used in preparing the positive electrode sheet are the same as those in Example 1, thereby finally obtaining the lithium-ion battery of this comparative example.

[0061] Test Example 1 1. Test Object This embodiment uses the lithium-ion batteries prepared in Examples 1-11 and Comparative Examples 1 and 2 as test objects.

[0062] 2. Test Items and Test Methods (1) Rate performance of lithium batteries The test object was subjected to a rate test, and the test method was as follows: At 25℃, it was charged with a constant current of 0.33 C to 4.25 V, and then charged with a constant voltage of 4.25 V until the current cutoff was 0.05 C; it was then discharged with a constant current of 0.33 C to 2.5 V, and the discharge capacity was recorded.

[0063] (2) Lithium battery cycle performance Cyclic performance testing was performed on the test subject using the following method: The test subject was placed in a 25°C constant temperature chamber for 1 hour, charged at a constant current of 1 C to 4.25 V, then charged at a constant voltage of 4.25 V to a current of 0.05 C, allowed to stand for 30 minutes, and then discharged at a constant current of 1 C to 2.5 V, allowed to stand for 30 minutes. This cycle test was repeated until the capacity dropped to 80% of the initial capacity, and then the subject was disassembled to observe the lithium plating at the R-corner.

[0064] (3) Safety performance Safety tests were conducted on the test objects in accordance with GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles".

[0065] 3. Test Results The test results for this test example are shown in Table 1. The test results show that the lithium plating in the R-corner region of the electrode assemblies provided in Examples 1 to 11 is significantly better than that in Comparative Examples 1 and 2. Specifically, the R-corner regions of Examples 1 to 11 only exhibit slight lithium plating, while the R-corner regions of Comparative Examples 1 and 2 show severe lithium plating. This difference is due to the clear differences in the structural design of the electrode assemblies among the three examples. In the electrode assemblies provided in Examples 1 to 11, only phosphate positive electrode active material is provided in the R-corner region, while the large surface area contains both phosphate and ternary positive electrode active materials. Although Comparative Example 1 is similar to the examples in terms of material types and uses a similar partitioning arrangement in the large surface area, its R-corner region also introduces a ternary positive electrode active material region, coexisting with the phosphate material region. Comparative Example 2 did not perform any partitioning design based on material types in the R-corner region and the large surface area; instead, it directly mixed the two active materials and coated them onto the entire positive electrode sheet.

[0066] The differences in lithium plating observed are closely related to whether the positive active material in the R-corner region of the electrode assembly consists solely of phosphate positive active material. In the electrode assemblies provided in Examples 1-11, the R-corner region entirely uses phosphate material with relatively low specific capacity, resulting in a higher local N / P ratio compared to the larger area. This effectively suppresses the tendency for lithium plating at the R-corner during cycling, extending the cycle life of the cell and improving safety performance. In contrast, the R-corner region of the electrode assembly provided in Comparative Example 1 contains ternary material, resulting in a lower local N / P ratio. Lithium ions are more likely to deposit at the R-corner during cycling, forming lithium dendrites, leading to severe lithium plating, which accelerates capacity decay and reduces the safety test pass rate. In Comparative Example 2, the lithium plating problem was more pronounced due to the complete lack of partitioning of the positive active material during electrode assembly preparation, resulting in lower overall electrochemical performance and safety. On the other hand, in the positive electrode sheets prepared in Examples 1-11, the R-corner region does not use ternary material at all, physically blocking the continuous thermal propagation path of the ternary material along the electrode winding direction, reducing the risk of thermal runaway propagation. In Comparative Examples 1 and 2, the presence of ternary materials in the R-angle region weakens this thermal propagation blocking mechanism, making thermal runaway more likely to spread, and thus their cycle performance and safety performance can only remain at a low level.

[0067] Comparing the test results of the electrode assemblies provided in Example 1 and Example 4 in this test example, the electrode assembly provided in Example 4 had a relatively lower number of cycles, and its safety test pass rate was also lower than that of the electrode assembly provided in Example 1. The difference between the two in the preparation process of the electrode assemblies is that in the positive electrode sheet prepared in Example 4, the positive active material layer in the large area is not layered in the z-direction, but consists of only one layer of positive active material; while in the positive electrode sheet prepared in Example 1, a first positive active material layer and a second positive active material layer are stacked in the z-direction in the large area, and the two layers are staggered, so that at least part of the projection of any ternary positive active material region in the z-direction overlaps with a phosphate positive active material region. In the positive active material layer of the electrode assembly in Example 1, because the ternary positive active material regions and the phosphate positive active material regions in different layers form an overlapping projection relationship in the z-direction, the relatively good thermal stability of the phosphate positive electrode material can form a local thermal buffer interface in the z-direction of the positive active material layer. This helps to mitigate the heat transfer along the z-direction that may be generated by the ternary cathode active material during cycling or abnormal conditions, thereby improving the cycle stability and thermal safety of the electrode assembly. In contrast, the cathode active material layer of the electrode assembly prepared in Example 4 does not employ the above-mentioned layered misalignment structure. During testing, the thermal buffering effect of the cathode active material layer in the z-direction is relatively limited, resulting in a lower performance in cycle life and safety test pass rate compared to the electrode assembly provided in Example 1.

[0068] Examples 1, 5, and 6 all employed a design in the preparation of electrode assemblies that included only phosphate-based positive electrode active material in the R-corner region of the positive electrode active material layer and a double-layered staggered structure in the large surface area. The main difference between the three lies in the spacing d between adjacent ternary positive electrode active material regions belonging to different layers on the composite surface of the first and second positive electrode active material layers. Specifically, d was set to 2 mm in Example 1, 0 mm in Example 5, and 2.5 mm in Example 6. In terms of cycle performance, the electrode assembly provided in Example 1 achieved the highest number of cycles. Regarding safety test pass rate, the electrode assembly provided in Example 1 was superior to that provided in Example 5. This demonstrates that the difference in d value leads to differences in the performance composition of the electrode assembly. When d is 0 mm (Example 5), the two ternary positive electrode active material regions belonging to different layers in the z-direction are directly connected on the two-layer composite surface, lacking the separation of the phosphate-based positive electrode active material region in between. This makes it easier for heat from the ternary cathode active material to be transferred between different layers along the z-direction of the cathode sheet, weakening the thermal buffering effect. Therefore, its safety test pass rate is relatively low among the three, and the cycle life is also shorter than that of Example 1. When d is 2.5 mm (Example 6), although the phosphate cathode active material region can effectively isolate the heat transfer between different layers of ternary cathode active material regions, the larger spacing exacerbates the non-uniformity of lithium intercalation caused by capacity differences between the spaced region and the surrounding adjacent regions. The uniformity of lithium ion intercalation during cycling is affected to a certain extent, so the number of cycles is lower than that of Example 1. In contrast, Example 1 controls d at 2 mm, which ensures that the phosphate cathode active material region forms an effective barrier between different layers of ternary cathode active material regions, thereby maintaining high thermal safety, and avoids the problem of non-uniform lithium intercalation caused by excessive spacing, so that the cycle life and safety performance are both well balanced. For the design of a positive electrode active material layer with only phosphate positive electrode active material in the R-corner region and a double-layer misaligned structure in the large area region, ensuring that d satisfies 0 mm < d ≤ 2 mm helps to achieve a balance between thermal spread suppression and lithium intercalation uniformity, thereby improving the overall performance of the electrode assembly.

[0069] For a cathode sheet that simultaneously incorporates both ternary and phosphate cathode active material regions, controlling the compaction density P2 of the phosphate cathode active material region to be lower than the compaction density P1 of the ternary cathode active material region allows the phosphate cathode active material region to maintain a relatively high porosity. This improves its internal ion transport efficiency, helps to reduce the difference in ion conductivity between the phosphate and ternary cathode active material regions, lowers the ion migration resistance at the interface between different material regions, and ultimately enhances the overall lithium-ion conductivity of the cathode active material layer, resulting in superior rate performance for the electrode assembly. The P1 / P2 ratios of the electrode assemblies in Examples 1 and 7 are 1.22 and 1.50, respectively. Compared to the electrode assemblies provided in Examples 8 and 9, the electrode assemblies provided in Examples 1 and 7 exhibit better rate performance and cycle life. The P1 / P2 ratio of the electrode assembly in Example 9 is 1.17, which is relatively low. This indicates that the phosphate cathode active material region has a high degree of compaction and relatively insufficient porosity, resulting in limited improvement in ion transport efficiency. Consequently, the 4C discharge capacity retention rate is relatively low, and the cycle life is shorter than that of Example 1. The P1 / P2 ratio of the electrode assembly in Example 8 is 1.54. Although the phosphate cathode active material region has higher porosity, the lower compaction density may affect the structural stability and continuity of the electron conduction path within the cathode active material layer, leading to a decrease in rate performance and a reduction in cycle life. For cathode sheets that simultaneously incorporate ternary and phosphate cathode active material regions, controlling the P1 / P2 ratio of the electrode assembly between 1.2 and 1.5 helps to achieve a balance between the ion transport efficiency of the phosphate cathode active material region and the overall structural stability, thus balancing the rate performance and cycle life of the electrode assembly.

[0070] Examples 1, 10, and 11 all employed a design where the R-corner region contained only phosphate positive electrode active material and the large-area region had a double-layer misaligned structure during the electrode assembly fabrication process. The main difference between the three lies in the conductivity of the phosphate positive electrode active material region. The difference between Examples 1 and 10 is that in Example 1, the mass fraction of the conductive agent in the phosphate positive electrode active material region is higher than that in the ternary positive electrode active material region, while in Example 10, the mass fraction of the conductive agent in both regions is the same. Example 1 effectively improved the electronic conductivity of the phosphate positive electrode active material region by increasing the conductive agent content, thereby balancing the conductivity difference between the phosphate and ternary positive electrode active material regions, reducing the contact resistance at the interface between different material regions, and improving the overall electronic conduction efficiency of the positive electrode active material layer. Therefore, the rate performance and cycle life of the electrode assembly of Example 1 are superior to those of the electrode assembly of Example 10. The difference between Example 1 and Example 11 is that Example 11 uses a carbon-coated phosphate cathode active material (carbon-coated lithium iron phosphate), while the phosphate cathode active material used in Example 1 is not carbon-coated. Carbon-coated phosphate cathode active material can also improve the conductivity of the phosphate cathode active material region, helping to narrow the conductivity gap between the phosphate cathode active material region and the ternary cathode active material region, reducing interfacial contact resistance, and further optimizing the overall electronic conduction efficiency of the cathode active material layer. Thanks to this design, the electrode assembly of Example 11 exhibits better rate performance and cycle life than the electrode assembly of Example 1. The above comparison shows that whether by increasing the proportion of conductive agent in the phosphate cathode active material region or using carbon-coated phosphate cathode active material, it is possible to further improve the rate performance and cycle life of electrode assemblies containing both phosphate and ternary cathode active materials while maintaining good safety performance.

[0071] Table 1. Test results of Test Case 1

[0072] Example 12 This embodiment refers to Example 1 to prepare a lithium-ion battery. 1. Fabrication of electrode components (1) Preparation of the positive electrode: S1. Prepare phosphate slurry and ternary slurry separately. The phosphate slurry uses lithium manganese iron phosphate as the phosphate positive electrode active material, with a composition of lithium manganese iron phosphate: conductive agent: binder = 88:10:2 by mass, and a solid content of 70wt%. The ternary slurry uses NCM622 as the ternary positive electrode active material, with a composition of NCM622: conductive agent: binder = 94:4:2 by mass, and a solid content of 74wt%.

[0073] S2. Perform the first layer coating and drying. The operation is similar to step S2 in Example 1. The ternary slurry and phosphate slurry prepared in this example are coated alternately along the width direction of the flat current collector 5 to form a first positive electrode active material layer 1 with a large surface area. In the first positive electrode active material layer 1, the ternary positive electrode active material region 3 and the phosphate positive electrode active material region 4 are along the width direction of the large surface area ( Figure 5 The materials are arranged alternately in opposite directions (as shown in the x direction). Compared with Example 1, the difference of the first positive electrode active material layer 1 prepared in this example is that: on the plane determined by the width direction of the large surface area and the z direction, the cross-sectional shape of the ternary positive electrode active material region 3 and the phosphate positive electrode active material region 4 is a right trapezoid. Along the width direction of the large surface area, the width of the long base of the right trapezoid is D', and the width of the short base is D (D'>D, D'-D=1 mm). The short base (D) of one ternary positive electrode active material region 3 is adjacent to the long base (D') of the adjacent phosphate positive electrode active material region 4, while the long base (D') of the ternary positive electrode active material region 3 is adjacent to the short base (D) of the phosphate positive electrode active material region 4 on the other side. At the same time, the thickness of the first positive electrode active material layer 1 and the phosphate positive electrode active material region 4 formed in the corresponding R-angle region are both controlled to be 50 μm.

[0074] S3. Perform the second layer coating and drying. The operation is similar to step S3 in Example 1. The ternary slurry and phosphate slurry prepared in this example are coated alternately along the width direction of the large area on the first positive electrode active material layer 1 to form a second positive electrode active material layer 2 covering a large area. The cross-sectional shape and internal arrangement of the second positive electrode active material layer 2 are the same as those of the first positive electrode active material layer 1 obtained in step S2 of this example. Figure 5 As shown, through coating control, the first positive electrode active material layer 1 and the second positive electrode active material layer 2 are configured such that, on the plane defined by the width direction of the large area and the z-direction, the short bottom edge (D) of the ternary positive electrode active material region 3 located in the first positive electrode active material layer 1 (or the second positive electrode active material layer 2) is adjacent to the long bottom edge (D') of the phosphate positive electrode active material region 4 located in the second positive electrode active material layer 2 (or the first positive electrode active material layer 1) and directly opposite it in the z-direction. Simultaneously, the thickness of both the second positive electrode active material layer 2 and the phosphate positive electrode active material region 4 formed in the corresponding R-angle region is controlled to be 50 μm.

[0075] S4. The positive electrode sheet after the above coating and drying steps are cold-pressed. The cold-pressing parameters are: temperature 25℃, roller pressure 3600kN / m, roller speed 27m / min. After cold pressing, the compaction density P1 of the ternary positive electrode active material region 3 in the positive electrode sheet is 3.32g / cm³. 3The compaction density P2 of region 4 of the phosphate positive electrode active material is 2.55 g / cm³. 3 .

[0076] (2) Preparation of negative electrode Except for the electrode thickness being changed to 180μm, the materials used, their proportions, and the operating steps are the same as in Example 1. (3) Assembly of electrode assembly The materials used, their proportions, and the operating steps are the same as in Example 1.

[0077] 2. Encased in a housing The materials used, their proportions, and the operating steps are the same as in Example 1.

[0078] Comparative Example 3 This comparative example uses Example 12 as a reference to prepare a lithium-ion battery. The difference from Example 12 is that, in preparing the positive electrode sheet in this comparative example, the positive electrode active material contained in the R-corner region also includes ternary positive electrode active material and phosphate positive electrode active material, and the arrangement of the ternary positive electrode active material region and the phosphate positive electrode active material region in this region is the same as the arrangement of the large area region in Example 12. That is, the positive electrode active material layer in this region is also composed of alternating ternary material region and phosphate material region in the z-direction.

[0079] Apart from the differences mentioned above, the materials used in this comparative example, their proportions, operating steps, and other materials used in preparing the positive electrode sheet are the same as those in Example 12, thereby finally obtaining the lithium-ion battery of this comparative example.

[0080] Comparative Example 4 This comparative example uses Example 12 as a reference to prepare a lithium-ion battery. The difference from Example 12 is that the positive electrode active material layer in this comparative example was not partitioned or layered during the preparation of the positive electrode sheet. Specifically, a ternary positive electrode active material (NCM622) and a phosphate positive electrode active material (lithium iron phosphate) were mixed and slurried. The resulting slurry had a mass ratio of NCM622:lithium iron phosphate:conductive agent:binder = 46.5:44:5.5:4. This slurry was then used to coat a single layer onto a flat current collector surface. The resulting positive electrode active material layer covered both the large surface area and the rounded corner area, with a thickness of 100 μm. After cold pressing, the compaction density of this positive electrode active material layer was 3.12 g / cm³. 3 Apart from the differences mentioned above, the materials used in this comparative example, their proportions, operating steps, and other materials used in preparing the positive electrode sheet are the same as those in Example 12, thereby finally obtaining the lithium-ion battery of this comparative example.

[0081] Example 13 This embodiment refers to Example 1 to prepare a lithium-ion battery. The difference between this embodiment and Example 1 lies in the preparation of the positive electrode sheet, as detailed below: 1. Fabrication of electrode assemblies (1) Preparation of the positive electrode: S1. Prepare phosphate slurry and ternary slurry separately. The phosphate slurry uses lithium manganese iron phosphate as the phosphate positive electrode active material, with a composition of lithium manganese iron phosphate: conductive agent: binder = 93:5:2 by mass, and a solid content of 70wt%. The ternary slurry uses NCM613 as the ternary positive electrode active material, with a composition of NCM613: conductive agent: binder = 94:4:2 by mass, and a solid content of 74wt%.

[0082] S2. Perform the first layer coating and drying. The operation is similar to step S2 in Example 1. The ternary slurry and phosphate slurry prepared in this example are coated alternately along the width direction of the flat current collector 5 to form the first positive electrode active material layer 1 over a large area. Compared with Example 1, the difference in the first positive electrode active material layer 1 obtained in this example is that: in the direction parallel to the width of the large area (… Figure 6 On the plane defined by the x-direction and z-direction, the cross-sectional shape of the ternary positive electrode active material region 3 and the phosphate positive electrode active material region 4 can be an isosceles trapezoid or a right trapezoid. Along the width direction of the large area, the width of the long base of the isosceles trapezoid is W' and the width of the short base is W (W' > W, (W'-W) / 2 = 1 mm), and the width of the long base of the right trapezoid is D' and the width of the short base is D (D' > D, D'-D = 1 mm). At the same time, the thickness of the first positive electrode active material layer 1 and the phosphate positive electrode active material region 4 formed in the corresponding R-angle region are both controlled to be 40 μm.

[0083] S3. Perform the second layer coating and drying. The operation is similar to step S3 in Example 1. The ternary slurry and phosphate slurry prepared in this example are coated alternately on the first positive electrode active material layer 1 along the width direction of the large area to form the second positive electrode active material layer 2 of the large area. On the plane determined by the width direction of the large area and the z-direction, the cross-sectional shape of the ternary positive electrode active material region 3 and the phosphate positive electrode active material region 4 of the second positive electrode active material layer 2 can be an isosceles trapezoid or a right trapezoid. Along the width direction of the large area, the width of the long base of the isosceles trapezoid is W' and the width of the short base is W (W' > W, (W'-W) / 2 = 1 mm), and the width of the long base of the right trapezoid is D' and the width of the short base is D (D' > D, D'-D = 1 mm). Through coating control, the first positive electrode active material layer 1 and the second positive electrode active material layer 2 are made such that the ternary positive electrode active material regions 3 belonging to the first positive electrode active material layer 1 and the second positive electrode active material layer 2 are staggered in the z-direction, as shown below. Figure 6As shown. Meanwhile, the thickness of the second positive electrode active material layer 2 and the phosphate positive electrode active material region 4 formed in the corresponding R-corner region are both controlled to be 40 μm.

[0084] S4. The positive electrode sheet after the above coating and drying steps are cold-pressed. The cold-pressing parameters are: temperature 25℃, roller pressure 3600kN / m, roller speed 27m / min. After cold pressing, the compaction density P1 of the ternary positive electrode active material region 3 in the positive electrode sheet is 3.32g / cm³. 3 The compaction density P2 of region 4 of the phosphate positive electrode active material is 2.55 g / cm³. 3 .

[0085] (2) Preparation of negative electrode Except for the electrode thickness being changed to 148μm, the materials used, their proportions, and the operating steps are the same as in Example 1.

[0086] (3) Assembly of electrode assembly The materials used, their proportions, and the operating steps are the same as in Example 1.

[0087] 2. Encased in a housing The materials used, their proportions, and the operating steps are the same as in Example 1.

[0088] Comparative Example 5 This comparative example uses Example 13 as a reference to prepare a lithium-ion battery. The difference from Example 13 is that, in preparing the positive electrode sheet in this comparative example, the positive electrode active material contained in the R-corner region also includes ternary positive electrode active material and phosphate positive electrode active material, and the arrangement of the ternary positive electrode active material region and the phosphate positive electrode active material region in this region is the same as the arrangement of the large area region in Example 13. That is, the positive electrode active material layer in this region is also composed of alternating ternary material region and phosphate material region in the z-direction.

[0089] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery in this comparative example are the same as those in Example 13, thereby finally obtaining the lithium-ion battery of this comparative example.

[0090] Comparative Example 6 This comparative example uses Example 13 as a reference to prepare a lithium-ion battery. The difference from Example 13 is that the positive electrode active material layer in this comparative example was not partitioned or layered during the preparation of the positive electrode sheet. Specifically, a ternary positive electrode active material (NCM622) and a phosphate positive electrode active material (lithium iron phosphate) were mixed to form a slurry. The resulting slurry had a mass ratio of NCM622:lithium iron phosphate:conductive agent:binder = 46.5:44:5.5:4. This slurry was then used to coat a single layer onto a flat current collector surface. The resulting positive electrode active material layer covered both the large surface area and the rounded corner area, with a thickness of 80 μm. After cold pressing, the compaction density of this positive electrode active material layer was 3.12 g / cm³. 3 Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery in this comparative example are the same as those in Example 13, thereby finally obtaining the lithium-ion battery of this comparative example.

[0091] Example 14 This embodiment refers to Example 1 to prepare a lithium-ion battery. The difference between this embodiment and Example 1 lies in the preparation of the positive electrode sheet, as detailed below: 1. Fabrication of electrode assemblies (1) Preparation of the positive electrode: S1. Prepare phosphate slurry and ternary slurry separately. The phosphate slurry uses lithium manganese iron phosphate as the phosphate positive electrode active material, with a composition of lithium manganese iron phosphate: conductive agent: binder = 88:10:2 by mass, and a solid content of 70wt%. The ternary slurry uses NCM712 as the ternary positive electrode active material, with a composition of NCM712: conductive agent: binder = 95:3:2 by mass, and a solid content of 74wt%.

[0092] S2. Perform the first layer coating and drying. The operation is similar to step S2 in Example 1. The ternary slurry and phosphate slurry prepared in this example are coated alternately along the width direction of the current collector 5 to form the first positive electrode active material layer 1 over a large area. Compared with Example 1, the difference in the first positive electrode active material layer 1 obtained in this example is that: in the direction parallel to the width of the large area (… Figure 7On the plane defined by the x-direction and z-direction, the cross-sectional shape of the ternary positive electrode active material region 3 and the phosphate positive electrode active material region 4 can be rectangular, isosceles trapezoidal, or right trapezoidal. Along the width direction of the large area, the side length of the rectangle is L, the width of the long base of the isosceles trapezoid is W', and the width of the short base is W (W' > W, (W'-W) / 2 = 1 mm), and the width of the long base of the right trapezoid is D', and the width of the short base is D (D' > D, D'-D = 1 mm). Meanwhile, the thickness of the first positive electrode active material layer 1 and the phosphate positive electrode active material region 4 formed in the corresponding R-angle region are both controlled to be 20 μm.

[0093] S3. Perform the second layer coating and drying. The operation is similar to step S3 in Example 1. The ternary slurry and phosphate slurry prepared in this example are coated alternately on the first positive electrode active material layer 1 along the width direction of the large area to form the second positive electrode active material layer 2 of the large area. On the plane determined by the width direction of the large area and the z-direction, the cross-sectional shape of the ternary positive electrode active material region 3 and the phosphate positive electrode active material region 4 of the second positive electrode active material layer 2 can be rectangular, isosceles trapezoidal, or right trapezoidal. Along the width direction of the large area, the side length of the rectangle is L, the width of the long base of the isosceles trapezoid is W', and the width of the short base is W (W' > W, (W'-W) / 2 = 1 mm), and the width of the long base of the right trapezoid is D', and the width of the short base is D (D' > D, D'-D = 1 mm). Through coating control, the first positive electrode active material layer 1 and the second positive electrode active material layer 2 are made such that the ternary positive electrode active material regions 3 belonging to the first positive electrode active material layer 1 and the second positive electrode active material layer 2 are staggered in the z-direction, as shown below. Figure 6 As shown. Meanwhile, the thickness of the second positive electrode active material layer 2 and the phosphate positive electrode active material region 4 formed in the corresponding R-corner region are both controlled to be 20 μm.

[0094] S4. The positive electrode sheet after the above coating and drying steps are cold-pressed. The cold-pressing parameters are: temperature 25℃, roller pressure 3600kN / m, roller speed 27m / min. After cold pressing, the compaction density P1 of the ternary positive electrode active material region 3 in the positive electrode sheet is 3.32g / cm³. 3 The compaction density P2 of region 4 of the phosphate positive electrode active material is 2.55 g / cm³. 3 .

[0095] (2) Preparation of negative electrode Except for the electrode thickness being changed to 80μm, the materials used, their proportions, and the operating steps are the same as in Example 1.

[0096] (3) Assembly of electrode assembly The materials used, their proportions, and the operating steps are the same as in Example 1.

[0097] 2. Encased in a housing The materials used, their proportions, and the operating steps are the same as in Example 1.

[0098] Comparative Example 7 This comparative example uses Example 14 as a reference to prepare a lithium-ion battery. The difference from Example 14 is that, in preparing the positive electrode sheet in this comparative example, the positive electrode active material contained in the R-corner region also includes ternary positive electrode active material and phosphate positive electrode active material, and the arrangement of the ternary positive electrode active material region and the phosphate positive electrode active material region in this region is the same as the arrangement of the large area region in Example 14. That is, the positive electrode active material layer in this region is also composed of alternating ternary material region and phosphate material region in the z-direction.

[0099] Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery in this comparative example are the same as those in Example 14, thereby finally obtaining the lithium-ion battery of this comparative example.

[0100] Comparative Example 8 This comparative example uses Example 14 as a reference to prepare a lithium-ion battery. The difference from Example 14 is that the positive electrode active material layer in this comparative example was not partitioned or layered during the preparation of the positive electrode sheet. Specifically, a ternary positive electrode active material (NCM622) and a phosphate positive electrode active material (lithium iron phosphate) were mixed and slurried. The resulting slurry had a mass ratio of NCM622:lithium iron phosphate:conductive agent:binder = 46.5:44:5.5:4. This slurry was then used to coat a single layer onto a flat current collector surface. The resulting positive electrode active material layer covered both the large surface area and the rounded corner area, with a thickness of 40 μm. After cold pressing, the compaction density of this positive electrode active material layer was 3.12 g / cm³. 3 Apart from the differences mentioned above, the other materials used in the preparation of the positive electrode sheet, their proportions, operating steps, and other materials used to prepare the lithium-ion battery in this comparative example are the same as those in Example 14, thereby finally obtaining the lithium-ion battery of this comparative example.

[0101] Test Example 2 1. Test Object This embodiment uses the lithium-ion batteries prepared in Examples 12-14 and Comparative Examples 3-8 as test objects.

[0102] 2. Test Items and Test Methods (1) Rate performance of lithium batteries The test object was subjected to a rate test, and the test method was as follows: At 25℃, it was charged with a constant current of 0.33 C to 4.25 V, and then charged with a constant voltage of 4.25 V until the current cutoff was 0.05 C; it was then discharged with a constant current of 0.33 C to 2.5 V, and the discharge capacity was recorded.

[0103] (2) Lithium battery cycle performance Cyclic performance testing was performed on the test subject using the following method: The test subject was placed in a 25°C constant temperature chamber for 1 hour, charged at a constant current of 1 C to 4.25 V, then charged at a constant voltage of 4.25 V to a current of 0.05 C, allowed to stand for 30 minutes, and then discharged at a constant current of 1 C to 2.5 V, allowed to stand for 30 minutes. This cycle test was repeated until the capacity dropped to 80% of the initial capacity, and then the subject was disassembled to observe the lithium plating at the R-corner.

[0104] (3) Safety performance Safety tests were conducted on the test objects in accordance with GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles".

[0105] 3. Test Results The test results for this test example are shown in Table 2. In this test example, the test objects provided in Example 12 are compared with those provided in Comparative Examples 3 and 4; the test objects provided in Example 13 are compared with those provided in Comparative Examples 5 and 6; and the test objects provided in Example 14 are compared with those provided in Comparative Examples 7 and 8. The variable settings for each comparison group are the same as those for Examples 1 to 11 in Test Example 1 relative to Comparative Examples 1 and 2. That is, the positive electrode active material in the R-corner region of the examples is entirely phosphate positive electrode active material, while the positive electrode active material in the R-corner region of the comparative examples contains ternary positive electrode active material or is not partitioned for different types of positive electrode active materials. Since different examples use different positive electrode active materials, the intrinsic properties of each group of materials differ; therefore, separate comparisons are more accurate.

[0106] The test results of this example show that the electrode assemblies provided in Examples 12, 13, and 14 all exhibited superior cycle life and safety test pass rates compared to the comparative examples in their respective comparison groups, with only slight lithium plating in the R-corner region. In contrast, the electrode assemblies in Comparative Examples 3-8 all showed severe lithium plating in the R-corner region. This trend is consistent with the conclusion in Test Example 1, indicating that even if the specific phosphate cathode active material or ternary cathode active material is changed, as long as phosphate cathode active material is used exclusively in the R-corner region and the two cathode active materials are reasonably partitioned in a large area, R-corner lithium plating can be effectively suppressed and the heat propagation path can be blocked. This improves the cycle stability and safety performance of the electrode assembly while maintaining a high energy density.

[0107] Table 2. Test results of Test Case 2

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. An electrode assembly comprising a positive electrode, a separator, and a negative electrode stacked together, characterized in that: The positive electrode, separator, and negative electrode are wound along the y-direction; the positive electrode includes a stacked positive active material layer and a positive current collector, and the positive active material layer includes an R-corner region and a large surface region; The R-corner region is the corner region formed by the positive electrode active material layer being wound along the y-direction, and the positive electrode active material contained therein is a phosphate positive electrode active material. The large surface area is a planar region that connects two adjacent R-angle regions in the y-direction, and the positive electrode active materials contained therein include phosphate positive electrode active materials and ternary positive electrode active materials.

2. The electrode assembly as described in claim 1, characterized in that: The large area includes several ternary cathode active material regions and several phosphate cathode active material regions. The cathode active material contained in the ternary cathode active material regions is a ternary cathode active material, and the cathode active material contained in the phosphate cathode active material regions is a phosphate cathode active material. The large surface area includes a first positive electrode active material layer and a second positive electrode active material layer stacked along the z-direction, wherein the z-direction is perpendicular to the large surface area. The first positive electrode active material layer and the second positive electrode active material layer each independently include a plurality of the ternary positive electrode active material regions and a plurality of the phosphate positive electrode active material regions; The first positive electrode active material layer and the second positive electrode active material layer are staggered in the z-direction, such that in the z-direction, at least a partial projection of any of the ternary positive electrode active material regions overlaps with one of the phosphate positive electrode active material regions.

3. The electrode assembly as described in claim 2, characterized in that: In the large area, the phosphate positive electrode active material region is provided between any adjacent ternary positive electrode active material regions to form an isolation.

4. The electrode assembly of claim 2, wherein: On the composite surface of the first positive electrode active material layer and the second positive electrode active material layer, the distance between any two adjacent ternary positive electrode active material regions belonging to different layers in the width direction of the large area is d, where 0 mm < d ≤ 2 mm.

5. The electrode assembly of claim 2, wherein the conductive material is a conductive adhesive. The electrode assembly satisfies at least one of the following: a, b, c: a. The compaction density of the ternary cathode active material region is P1, and the compaction density of the phosphate cathode active material region is P2, where P2 < P1; b. The mass fraction of the conductive agent in the phosphate positive electrode active material region is higher than the mass fraction of the conductive agent in the ternary positive electrode active material region; c. The phosphate positive active material contained in the positive active material layer includes carbon-coated phosphate positive active material.

6. The electrode assembly of claim 5, wherein: The ternary cathode active material region and the phosphate cathode active material region satisfy P1 / P2=1.2~1.

5.

7. The electrode assembly as described in claim 5, characterized in that: The mass fraction of the conductive agent in the phosphate positive electrode active material region is 4.9% to 10%, and the mass fraction of the conductive agent in the ternary positive electrode active material region is 2.9% to 4.1%.

8. The electrode assembly of claim 2, wherein: The thickness of the first positive electrode active material layer is 20–50 μm, and the thickness of the second positive electrode active material layer is 20–50 μm.

9. The electrode assembly of claim 2, wherein: On the plane formed by the width direction of the large area and the z-direction, the cross-sectional shape of the ternary positive electrode active material region and the phosphate positive electrode active material region is at least one of parallelogram, rectangle, trapezoid or irregular quadrilateral, and the cross-sectional shapes of the ternary positive electrode active material region and the phosphate positive electrode active material region are the same or different.

10. A battery, characterized by: The battery includes the electrode assembly as described in any one of claims 1 to 9.

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