Composite cells and batteries containing them

Abstract

To provide a composite cell that sufficiently exercises a synergy superiority of a positive electrode active material of a different type, and further improve an energy density of a battery, a rate characteristic, and a cycle performance.SOLUTION: A composite cell contains a positive electrode sheet, and each positive electrode sheet satisfies a ratio of a unit area capacity and a ratio of a unit area capacity of the other one of the positive electrode sheets so as to be 0.9 to 1.1. Each positive electrode sheet contains a first positive electrode sheet. A positive electrode active material contained in the first positive electrode sheet contains a first positive electrode active material and a second positive electrode active material. An energy density of the first positive electrode active material is larger than that of the second positive electrode active material. When a mass amount of the first positive electrode active material to be contained in the first positive electrode sheet is m1, and a total mass of the positive electrode active material contained to the first positive electrode sheet is m0, the following equation is satisfied. A mean one surface density of a positive electrode active coating is 50 to 650 g / m2, and a ratio surface resistance is 0.0001 to 0.1500 Ω / mm2*g.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present invention belongs to the field of battery technology, and specifically relates to a composite cell and a battery including the same. 【Background Art】 【0002】 The mainstream cathode materials for lithium-ion batteries mainly include oxide-based cathode active material systems and phosphate-based cathode active material systems. Oxide-based cathode active materials have high energy density but low structural stability, while phosphate-based cathode active materials have low energy density but long cycle life, and obvious advantages in terms of cost and safety. How to fully utilize the complementary advantages of different materials has always been a difficult problem in the industry. In the current industry, the blending method of directly coating the cathode slurry formed by mixing different types of cathode active materials on the surface of the current collector to produce the cathode sheet is common. However, due to the differences in the particle size and surface energy of different types of cathode active materials, the mixed slurry agglomerates. In the multi-layer coating method, the above problems can be avoided to a certain extent. However, when the difference in the ratio of different types of cathode active materials is large, the coating surface density of relatively small materials is too small to realize the coating process. 【0003】 Based on this, how to integrate different types of cathode sheets in the same cell and fully utilize the synergistic advantages of different types of cathode active materials is a technical problem that those skilled in the art should urgently solve in their research. 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 The present invention provides a composite cell and a battery including the same, so as to fully utilize the synergistic advantages of different types of cathode active materials and further improve the energy density, rate performance, and cycle performance of the battery. 【Means for Solving the Problems】 【0005】 According to a first aspect of the present invention, a composite cell is provided, the composite cell includes positive electrode sheets, the number of positive electrode sheets is greater than 1, each positive electrode sheet satisfies the condition that the ratio of its unit area capacity to the unit area capacity of any one other positive electrode sheet is 0.9 to 1.1, the positive electrode sheets include a first positive electrode sheet, the positive electrode active material contained in the first positive electrode sheet includes a first positive electrode active material and a second positive electrode active material, where the energy density of the first positive electrode active material is greater than the energy density of the second positive electrode active material, the mass of the first positive electrode active material contained in each first positive electrode sheet is less than the mass of the second positive electrode active material, let the mass of the first positive electrode active material contained in the first positive electrode sheet be m1, and the total mass of the positive electrode active material contained in the first positive electrode sheet be m0. 【number】 The number of layers of the positive electrode active coating provided on each first positive electrode sheet is greater than 1, and the average single-sided surface density of the positive electrode active coating is 50-650 g / m². 2 The specific resistance is 0.0001 to 0.1500 Ω / mm². 2 The positive electrode active coating comprises a first positive electrode coating and a second positive electrode active coating, the positive electrode active material contained in the first positive electrode active coating is composed of the first positive electrode active material, and the positive electrode active material contained in the second positive electrode active coating is composed of the second positive electrode active material. 【0006】 In the composite cell according to the present invention, by controlling the ratio of positive electrode active material in the first positive electrode sheet and the surface density and specific surface resistance of the first positive electrode sheet, the potential distribution of the first positive electrode sheet is made uniform, which is advantageous in mitigating the lithium deposition phenomenon caused by excessive local current density in the electrode sheet, and is also advantageous in improving the energy density of the electrode sheet. Furthermore, the capacitance balance between different positive electrode sheets in the composite cell is nearly achieved, further ensuring uniformity of the current density of the composite cell and reducing the impedance level of the electrode sheet. Based on this, the first positive electrode sheet according to the present invention has a stable structure, can fully demonstrate the advantages of different positive electrode active materials, can effectively mitigate the problems of impedance and current inequality that occur between different types of positive electrode active materials in the composite cell, and enables the composite cell to possess excellent energy density, high and low temperature performance, and cycle performance. 【0007】 If the mass proportion of the first positive electrode active material is too low, the precision of the coating process is limited, processing problems are likely to occur, and the non-uniform distribution of lithium ion concentration and potential is evident during the high-magnification charge-discharge process, making lithium deposition more likely. If the mass proportion of the first positive electrode active material is too high, it is detrimental to the structural stability of the first positive electrode sheet and increases costs. 【0008】 If the surface density and specific surface resistance of the first positive electrode sheet are too high, the electron transmission path becomes longer, the transmission speed slows down, the electronic conductivity of the electrode sheet decreases, and delamination is more likely to occur between the active material and the current collector due to the large volume effect during lithium ion insertion / removal, making the structure of the electrode sheet unstable. If the surface density and specific surface resistance of the first positive electrode sheet are too low, the coating accuracy of the electrode sheet is limited, processing problems are more likely to occur, it is detrimental to the uniformity of the lithium ion insertion / removal process, and the energy density of the cell decreases. 【0009】 Specifically, the average surface density of the positive electrode active coating provided on the positive electrode sheet is Di, the average gram volume of the positive electrode active material contained in the positive electrode sheet is Ci, the average initial efficiency of the positive electrode active material is Ei, the average mass ratio of the positive electrode active material is Wi, and its unit area volume Qi = Di* Ci * It is Wi / Ei. 【0010】 Specifically, the specific surface resistance of the positive electrode active coating = the surface resistance of the positive electrode active coating / the mass of the positive electrode active coating. 【0011】 Preferably, the positive electrode sheet further includes a second positive electrode sheet, and the average single-sided surface density of the positive electrode active coating provided on the second positive electrode sheet is 65 to 700 g / m 2 and the specific surface resistance is 0.0002 to 0.2000 Ω / mm 2 ·g. The combination effect of the second positive electrode sheet with a specific surface density and specific surface resistance and the above-mentioned first positive electrode sheet is excellent, and the second positive electrode sheet can exhibit a synergistic advantage with the first positive electrode sheet, ensuring the uniformity of the current density between different positive electrode sheets, and avoiding phenomena such as destabilization of the electrode sheet structure, precipitation of lithium, and polarization due to poor combination effect of the electrode sheets, thereby improving the overall energy density, high and low temperature performance, and cycle performance of the composite cell according to the present invention. 【0012】 Preferably, 【Number】 It is. 【0013】 Preferably, the average single-sided surface density of the positive electrode active coating provided on the first positive electrode sheet is 100 to 500 g / m 2 and the specific surface resistance is 0.0001 to 0.1200 Ω / mm 2 ·g. 【0014】 Preferably, the average single-sided surface density of the positive electrode active coating provided on the second positive electrode sheet is 200 to 600 g / m 2 and the specific surface resistance is 0.0002 to 0.1600 Ω / mm 2 ·g. 【0015】 Preferably, in the composite cell, the total mass of the first positive electrode active material is M1, and the total mass of the positive electrode active material is M0, 【number】 By rationally adjusting the content of the first positive electrode active material in the composite cell, it is advantageous to improve the combined effect between different positive electrode active materials, achieve overall uniformity of the current density of the composite cell, and further improve the energy density and cycle performance of the battery by allowing positive electrode active materials with different energy densities to exert a synergistic advantage. 【0016】 Preferably, the first positive electrode active material is a ternary positive electrode material, and the second positive electrode active material comprises at least one of lithium iron phosphate and lithium manganese iron phosphate. 【0017】 Preferably, on the same side of the current collector of the first positive electrode sheet, a positive electrode active coating formed of a first active material and a positive electrode active coating formed of a second positive electrode active material are sequentially provided along a direction away from the surface of the current collector. 【0018】 Preferably, the positive electrode active material used in the second positive electrode sheet includes one of lithium iron phosphate, lithium iron manganese phosphate, and lithium manganate. 【0019】 According to another aspect of the present invention, a battery including the above-mentioned composite cell is provided. 【0020】 Preferably, the composite cell includes a negative electrode sheet, and the negative electrode active material used in the negative electrode sheet includes a carbon negative electrode material and a non-carbon negative electrode material, where the carbon negative electrode material includes at least one of artificial graphite, natural graphite, hard carbon, and soft carbon, and the non-carbon negative electrode material includes at least one of silicon-based material, titanium-based material, and tin-based material. [Brief explanation of the drawing] 【0021】 [Figure 1] These are schematic diagrams of the composite cell structure in Examples 1-14 and Comparative Examples 2-4. [Figure 2]This is a schematic diagram of the structure of a composite cell in Comparative Example 1. In the attached drawing above, the correspondence between technical features and reference numerals is as follows: 1-1 second positive electrode sheet, 1-2 separator, 1-3 negative electrode sheet, 1-4 first positive electrode sheet, 1-41 first positive electrode active coating, 1-42 second positive electrode active coating, 2-1 second positive electrode sheet B, 2-2 separator, 2-3 negative electrode sheet, 2-4 second positive electrode sheet C. [Modes for carrying out the invention] 【0022】 To enable those skilled in the art to better understand the present invention, the following clearly and completely describes the technical aspects in the embodiments of the present invention. Clearly, the described embodiments are only some, not all, embodiments of the present invention. 【0023】 Example 1 【0024】 This embodiment provides a battery, the method for preparing it is as follows: 【0025】 1. Preparation of the second positive electrode sheet A1-1 A positive electrode slurry A is prepared by uniformly mixing lithium iron phosphate, PVDF binder, and acetylene black conductive agent in a mass ratio of 98:1:1. The positive electrode slurry A is applied to both sides of the positive electrode current collector and dried to form a positive electrode active coating A, and the average single-sided surface density S of the positive electrode active coating A is determined. A It is 210g / m 2 The positive electrode sheet prepared in this manner will be referred to as the second positive electrode sheet A1-1, and the specific surface resistance of the second positive electrode sheet A1-1 is 0.1230 Ω / mm². 2 It is g. 【0026】 2. Preparation of the first positive electrode sheet D1 1-4 Positive electrode slurry A is prepared by uniformly mixing lithium iron phosphate, binder PVDF, and conductive agent acetylene black in a mass ratio of 98:1:1. Positive electrode slurry C is prepared by uniformly mixing ternary positive electrode material, binder PVDF, and conductive agent acetylene black in a mass ratio of 90:5:5. Then, positive electrode slurry C is applied to both sides of the positive electrode current collector and dried to form the first positive electrode active coating 1-41. Next, positive electrode slurry A is applied to the surface of the first positive electrode active coating 1-41 and dried to form the second positive electrode active coating 1-42. The second positive electrode active coating 1-41 and the second positive electrode active coating 1-42 together constitute a composite positive electrode active coating provided on the first positive electrode sheet D1. The first positive electrode sheet prepared in this manner is denoted as the first positive electrode sheet D1 1-4. In the first positive electrode sheet D1 1-4, the average single-sided surface density S of the composite positive electrode active coating. D1 It is 165g / m² 2 Therefore, the specific resistance R D1 This is 0.0500Ω / mm 2 ·g and 【number】 Here, let m1 be the mass of the first positive electrode active material (ternary positive electrode material) contained in the first positive electrode sheet D1 1-4, and let m0 be the total mass of the positive electrode active material contained in the first positive electrode sheet D1 1-4. 【0027】 3. Preparation of composite cells A schematic diagram of the composite cell structure is shown in Figure 1. The composite cell is constructed by sequentially stacking separator 1-2, negative electrode sheet 1-3, separator 1-2, second positive electrode sheet A 1-1, separator 1-2, negative electrode sheet 1-3, separator 1-2, first positive electrode sheet D1 1-4, separator 1-2, and negative electrode sheet 1-3 (where the second positive electrode sheet A 1-1 consists of 6 sheets and the first positive electrode sheet D1 1-4 consists of 44 sheets). 【number】 The following conditions are met, where M1 is the mass of the first positive electrode active material (ternary positive electrode material) in the composite cell, M0 is the total mass of all positive electrode active materials in the composite cell, and composite cell 1 is 【number】 The following conditions are met, and the unit area capacity of the first positive electrode sheet D1 1-4 is Q D1 The unit area capacity of the second positive electrode sheet A 1-1 is set to Q. A Let's assume that. 【0028】 4. Battery preparation The composite cells are placed in a battery housing, then the battery housing is subjected to processes such as tab welding and firing. After passing the moisture content test, an appropriate amount of electrolyte is injected into the battery housing, it is packaged, and then aged, chemically converted, and evaporated to prepare the battery. 【0029】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0030】 Example 2 【0031】 This embodiment provides a battery, the method for preparing it is as follows: 【0032】 1. Preparation of the second positive electrode sheet B 1-1 Positive electrode slurry B is prepared by uniformly mixing manganese iron lithium phosphate, PVDF binder, and acetylene black conductive agent in a mass ratio of 98:1:1. Positive electrode slurry B is applied to both sides of the positive electrode current collector and dried to form positive electrode active coating B, and the average single-sided surface density S of the positive electrode active coating B is determined. B It is 175g / m 2 Thus, the positive electrode sheet prepared in this manner will be denoted as the second positive electrode sheet B1-1, and the specific surface resistance R of the second positive electrode sheet B1-1 is... B It has a resistance of 0.1230Ω / mm 2 It is g. 【0033】 2. Preparation of the first positive electrode sheet D2 1-4 Positive electrode slurry B is prepared by uniformly mixing lithium manganese iron phosphate, PVDF binder, and acetylene black conductive agent in a mass ratio of 98:1:1. Positive electrode slurry C is prepared by uniformly mixing ternary positive electrode material, PVDF binder, and acetylene black conductive agent in a mass ratio of 90:5:5. Then, positive electrode slurry C is applied to both sides of the positive electrode current collector and dried to form the first positive electrode active coating 1-41. Next, positive electrode slurry B is applied to the surface of the first positive electrode active coating 1-41 and dried to form the second positive electrode active coating 1-42. The first positive electrode active coating 1-41 and the second positive electrode active coating 1-42 together constitute a composite positive electrode active coating provided on the first positive electrode sheet D2 1-4, and the first positive electrode sheet prepared in this manner is referred to as the first positive electrode sheet D2 1-4. In the first positive electrode sheet D2 1-4, the average single-sided surface density S of the composite positive electrode active coating. D2 It is 160g / m 2 Therefore, the specific resistance R D1 This is 0.0800Ω / mm 2 ·g and 【number】 Here, let m1 be the mass of the first positive electrode active material (ternary positive electrode material) contained in the first positive electrode sheet D2 1-4, and let m0 be the total mass of the positive electrode active material contained in the first positive electrode sheet D2 1-4. 【0034】 3. Preparation of composite cells A schematic diagram of the composite cell structure is shown in Figure 1. The composite cell is constructed by sequentially stacking separator 1-2, negative electrode sheet 1-3, separator 1-2, second positive electrode sheet B 1-1, separator 1-2, negative electrode sheet 1-3, separator 1-2, first positive electrode sheet D2 1-4, separator 1-2, and negative electrode sheet 1-3 (where the second positive electrode sheet B 1-1 consists of 6 sheets and the first positive electrode sheet D2 1-4 consists of 44 sheets). 【number】 The following conditions are met, where M1 is the mass of the first positive electrode active material (ternary positive electrode material) in the composite cell, M0 is the total mass of all positive electrode active materials in the composite cell, and the composite cell is 【number】 The following conditions are met, and the unit area capacity of the first positive electrode sheet D2 1-4 is Q D2 The unit area capacity of the second positive electrode sheet B 1-1 is set to Q. B Let's assume that. 【0035】 4. Battery preparation The composite cells are placed in a battery housing, then the battery housing is subjected to processes such as tab welding and firing. After passing the moisture content test, an appropriate amount of electrolyte is injected into the battery housing, it is packaged, and then aged, chemically converted, and evaporated to prepare the battery. 【0036】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0037】 Example 3 【0038】 This embodiment provides a battery, the method for preparing it is as follows: 【0039】 1. Preparation of the second positive electrode sheet A1-1 For the preparation method of the second positive electrode sheet A, refer to the preparation of the second positive electrode sheet A in Example 1. 【0040】 2. Preparation of the first positive electrode sheet D2 1-4 For the preparation method of the first positive electrode sheet D2, refer to the preparation of the first positive electrode sheet D2 in Example 2. 【0041】 3. Preparation of composite cells A schematic diagram of the composite cell structure is shown in Figure 1. The composite cell is constructed by sequentially stacking separator 1-2, negative electrode sheet 1-3, separator 1-2, second positive electrode sheet A 1-1, separator 1-2, negative electrode sheet 1-3, separator 1-2, first positive electrode sheet D2 1-4, separator 1-2, and negative electrode sheet 1-3 (where there are 6 second positive electrode sheets A 1-3 and 44 first positive electrode sheets D2 1-4), and the composite cell is constructed as follows: 【number】 The following conditions are met, where M1 is the mass of the first positive electrode active material (ternary positive electrode material) in the composite cell, and M0 is the total mass of all positive electrode active materials in the composite cell. 【number】 The unit area capacitance of the first positive electrode sheet D2 1-4 is Q. D2 The unit area capacity of the second positive electrode sheet A 1-1 is set to Q. A Let's assume that. 【0042】 4. Battery preparation The composite cells are placed in a battery housing, then the battery housing is subjected to processes such as tab welding and firing. After passing the moisture content test, an appropriate amount of electrolyte is injected into the battery housing, it is packaged, and then aged, chemically converted, and evaporated to prepare the battery. 【0043】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0044】 Example 4 This embodiment provides a battery, the method for preparing it is as follows: 【0045】 1. Preparation of the second positive electrode sheet A1-1 For the preparation method of the second positive electrode sheet A, refer to the preparation of the second positive electrode sheet A in Example 1. 【0046】 2. Preparation of the first positive electrode sheet D3 1-4 Positive electrode slurry C is prepared by uniformly mixing a ternary positive electrode material, a binder PVDF, and a conductive agent acetylene black in a mass ratio of 90:5:5. Positive electrode slurry D is prepared by uniformly mixing lithium manganese oxide, a binder PVDF, and a conductive agent acetylene black in a mass ratio of 94:3:3. Then, positive electrode slurry C is applied to both sides of the positive electrode current collector and dried to form a first positive electrode active coating 1-41. Next, positive electrode slurry D is applied to the surface of the first positive electrode active coating 1-41 and dried to form a second positive electrode active coating 1-42. The first positive electrode active coating 1-41 and the second positive electrode active coating 1-42 together constitute a composite positive electrode active coating provided on the first positive electrode sheet D3 1-4, and the first positive electrode sheet prepared in this manner is referred to as the first positive electrode sheet D3 1-4. In the first positive electrode sheet D3 1-4, the average single-sided surface density S of the composite positive electrode active coating. D3 It is 175g / m 2 Therefore, the specific resistance R D1 This is 0.1000Ω / mm 2 ·g and 【number】 Here, let m1 be the mass of the first positive electrode active material (ternary positive electrode material) contained in the first positive electrode sheet D3 1-4, and let m0 be the total mass of the positive electrode active material contained in the first positive electrode sheet D3 1-4. 【0047】 3. Preparation of composite cells A schematic diagram of the composite cell structure is shown in Figure 1. The composite cell is constructed by sequentially stacking separator 1-2, negative electrode sheet 1-3, separator 1-2, second positive electrode sheet A 1-1, separator 1-2, negative electrode sheet 1-3, separator 1-2, first positive electrode sheet D3 1-4, separator 1-2, and negative electrode sheet 1-3 (where the second positive electrode sheet A 1-1 consists of 6 sheets and the first positive electrode sheet D3 1-4 consists of 44 sheets). 【number】 The following conditions are met, and the total mass of the small number of positive electrode active materials (ternary positive electrode material) in the composite cell is m, the total mass of all positive electrode active materials in the composite cell is M, and the composite cell is 【number】 The following conditions are met, and the unit area capacity of the first positive electrode sheet D3 1-4 is Q D3 The unit area capacity of the second positive electrode sheet A 1-1 is set to Q. A Let's assume that. 【0048】 4. Battery preparation The composite cells are placed in a battery housing, then the battery housing is subjected to processes such as tab welding and firing. After passing the moisture content test, an appropriate amount of electrolyte is injected into the battery housing, it is packaged, and then aged, chemically converted, and evaporated to prepare the battery. 【0049】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0050】 Example 5 【0051】 This embodiment prepares a battery with reference to Example 1, and the difference between this embodiment and Example 1 is as follows: In the first positive electrode sheet D1 1-4, 【number】 And in a composite cell, 【number】 Aside from the differences mentioned above, the materials and process procedures used in this embodiment are identical to those in Example 1. 【0052】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0053】 Example 6 【0054】 This embodiment prepares a battery with reference to Example 1, and the difference between this embodiment and Example 1 is as follows: In the first positive electrode sheet D1 1-4, 【number】 And in a composite cell, 【number】 Aside from the differences mentioned above, the materials and process procedures used in this embodiment are identical to those in Example 1. 【0055】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0056】 Example 7 【0057】 This embodiment prepares a battery with reference to Example 1, and the difference between this embodiment and Example 1 is as follows: In the first positive electrode sheet D1 1-4, 【number】 And in a composite cell, 【number】 Aside from the differences mentioned above, the materials and process procedures used in this embodiment are identical to those in Example 1. 【0058】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0059】 Example 8 【0060】 This embodiment prepares a battery with reference to Example 1, and the difference between this embodiment and Example 1 is as follows: In the first positive electrode sheet D1 1-4, 【number】 And in a composite cell, 【number】 Aside from the differences mentioned above, the materials and process procedures used in this embodiment are identical to those in Example 1. 【0061】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0062】 Example 9 【0063】 This embodiment prepares a battery in reference to Example 1, and the differences between this embodiment and Example 1 are as follows: In the second positive electrode sheet A1-1, the average single-sided surface density of the positive electrode active coating A is 50 g / m². 2 Therefore, the specific resistance is 0.0001 Ω / mm². 2 ·g. Aside from the differences mentioned above, the materials and process operations used in this embodiment are in exact agreement with those in Example 1. 【0064】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0065】 Example 10 【0066】 This embodiment prepares a battery with reference to Example 1, and the differences between this embodiment and Example 1 are as follows: In the second positive electrode sheet A1-1, the average single-sided surface density of the positive electrode active coating A is 65 g / m². 2 Therefore, the specific resistance is 0.0002 Ω / mm². 2 ·g. Aside from the differences mentioned above, the materials and process operations used in this embodiment are in exact agreement with those in Example 1. 【0067】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0068】 Example 11 【0069】 This embodiment prepares a battery in reference to Example 1, and the differences between this embodiment and Example 1 are as follows: In the second positive electrode sheet A 1-1, the average single-sided surface density of the positive electrode active coating A is 700 g / m². 2 The specific resistance is 0.2Ω / mm². 2 ·g. Aside from the differences mentioned above, the materials and process operations used in this embodiment are in exact agreement with those in Example 1. 【0070】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0071】 Example 12 【0072】 This embodiment prepares a battery with reference to Example 1, and the differences between this embodiment and Example 1 are as follows: In the second positive electrode sheet A 1-1, the average single-sided surface density of the positive electrode active coating A is 750 g / m². 2 The specific resistance is 0.25 Ω / mm². 2 ·g. Aside from the differences mentioned above, the materials and process operations used in this embodiment are in exact agreement with those in Example 1. 【0073】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0074】 Example 13 【0075】 This embodiment prepares a battery with reference to Example 1, and the difference between this embodiment and Example 1 is as follows: In the first positive electrode sheet D1 1-4, the surface density S of the composite positive electrode active coating D1 It is 650g / m 2 Therefore, the specific resistance R D1 This is 0.0001Ω / mm 2 ·g 2 Aside from the differences mentioned above, the materials and process procedures used in this embodiment are identical to those in Example 1. 【0076】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0077】 Example 14 【0078】 This embodiment prepares a battery with reference to Example 1, and the difference between this embodiment and Example 1 is as follows: In the first positive electrode sheet D1 1-4, the surface density S of the composite positive electrode active coating D1 It is 50g / m 2 Therefore, the specific resistance R D1 This is 0.0500Ω / mm 2 ·g 2 Aside from the differences mentioned above, the materials and process procedures used in this embodiment are identical to those in Example 1. 【0079】 A schematic diagram of the structure of the composite cell prepared in this embodiment is shown in Figure 1. 【0080】 Comparative Example 1 【0081】 This comparative example provides a battery, the method for which it is prepared is as follows: 【0082】 1. Preparation of the second positive electrode sheet B 2-1 Positive electrode slurry B is prepared by uniformly mixing manganese iron lithium phosphate, PVDF binder, and acetylene black conductive agent in a mass ratio of 98:1:1. Positive electrode slurry B is applied to both sides of the positive electrode current collector and dried to form positive electrode active coating B, and the average single-sided surface density S of the positive electrode active coating B is determined. B It is 175g / m 2 The specific resistance is 0.1200 Ω / mm². 2 ·g is the positive electrode sheet label prepared in this manner, and the positive electrode sheet label prepared in this manner is the second positive electrode sheet B 2-1. 【0083】 2. Preparation of the second positive electrode sheet C2-4 A ternary material, a PVDF binder, and an acetylene black conductive agent are uniformly mixed in a mass ratio of 90:5:5 to prepare a positive electrode slurry C. The positive electrode slurry C is applied to both sides of the positive electrode current collector and dried to form a positive electrode active coating C. The average single-sided surface density S of the positive electrode active coating C is then determined. C It is 150g / m 2The specific resistance is 0.1250 Ω / mm². 2 ·g is the positive electrode sheet label prepared in this manner, and the positive electrode sheet label prepared in this manner is the second positive electrode sheet C2-4. 【0084】 3. Preparation of composite cells A schematic diagram of the composite cell structure is shown in Figure 2. The composite cell is stacked sequentially as follows: separator 2-2, negative electrode sheet 2-3, second positive electrode sheet B 2-1, separator 2-2, negative electrode sheet 2-3, separator 2-2, second positive electrode sheet C 2-4, separator 2-2, negative electrode sheet 2-3 (where there are 44 second positive electrode sheets B 2-1 and 6 second positive electrode sheets C 2-4), and composite cell 1 is, 【number】 The following conditions are met, and the unit area capacity of the second positive electrode sheet C 2-4 is Q C The unit area capacity of the second positive electrode sheet B 2-1 is set to Q. B Let's assume that. 【0085】 4. Battery preparation The composite cells are placed in a battery housing, then the battery housing is subjected to processes such as tab welding and firing. After passing the moisture content test, an appropriate amount of electrolyte is injected into the battery housing, it is packaged, and then aged, chemically converted, and evaporated to prepare the battery. 【0086】 A schematic diagram of the structure of the composite cell prepared in this comparative example is shown in Figure 2. 【0087】 Comparative Example 2 【0088】 In this comparative example, the battery was prepared in reference to Example 1, and the difference between this comparative example and Example 1 is as follows: In the first positive electrode sheet D1 1-4, 【number】 And in a composite cell, 【number】 Aside from the differences mentioned above, the materials and process operations used in this comparative example are exactly the same as those in Comparative Example 1. 【0089】 A schematic diagram of the structure of the composite cell prepared in this comparative example is shown in Figure 1. 【0090】 Comparative Example 3 【0091】 In this comparative example, a battery was prepared in reference to Example 1, and the difference between this comparative example and Example 1 is as follows: In the first positive electrode sheet D1 1-4, the average single-sided surface density S of the composite positive electrode active coating. D1 It is 30g / m 2 Therefore, the specific resistance R D1 This is 0.00007Ω / mm 2 ·g. Aside from the differences mentioned above, the materials and process operations used in this comparative example are exactly the same as those in Comparative Example 1. 【0092】 A schematic diagram of the structure of the composite cell prepared in this comparative example is shown in Figure 1. 【0093】 Comparative Example 4 【0094】 In this comparative example, a battery was prepared in reference to Example 1, and the difference between this comparative example and Example 1 is as follows: In the first positive electrode sheet D1 1-4, the surface density S of the composite positive electrode active coating D1 It is 700g / m 2 Therefore, the specific resistance R D1 It is 0.20Ω / mm 2 ·g. Aside from the differences mentioned above, the materials and process operations used in this comparative example are exactly the same as those in Comparative Example 1. 【0095】 A schematic diagram of the structure of the composite cell prepared in this comparative example is shown in Figure 1. 【0096】 Test example 【0097】 1. Subjects In this test example, the batteries prepared in Examples 1-14 and Comparative Examples 1-4 will be used as test subjects. 【0098】 2. Exam Content 【0099】 (1) Energy density The test battery was charged to 4.25V with a constant current and voltage of 0.33C, cut off at 0.02C, and discharged to 2.8V at 0.33C. The capacity, average voltage, and cell mass were recorded, and the energy density of the battery was calculated using the following formula: Energy density = Capacity * Average voltage / Battery mass. 【0100】 (2) DC impedance The test battery was charged to 4.25V with a constant current and voltage of 0.33C, cut off at 0.02C, discharged at 0.33C for 90 minutes, left standing for 10 minutes, the end voltage V1 was recorded, and then discharged at 2C (current I) for 10 seconds, the end voltage V2 was recorded, and the DC impedance of the sodium-ion battery was calculated using the following formula: DC impedance = |V1 - V2| / I. 【0101】 (3) Cycle performance The test battery is placed in a 45°C incubator, charged with a constant current and voltage of 1C, cutoff at 0.02C, and then discharged at 1C, cycling to 80% SOC, and the number of cycles is recorded. 【0102】 3. Test Results [Table 1] [Table 2] 【0103】 The results of the correlation performance tests for the batteries prepared in Examples 1-14 and Comparative Examples 1-4 are shown in Table 1. 【0104】 Comparing the performance test results corresponding to Example 1 and Comparative Example 1, as can be seen from Table 1, under the same conditions for other materials and operations used to prepare the batteries, the batteries prepared in Examples 1 to 14 have low impedance levels and superior energy density and cycle performance. In contrast, the composite cell prepared in Comparative Example 1 is provided with only a second positive electrode sheet, and the cycle performance of the battery obtained in this manner is clearly lower than that of the battery prepared in Example 1. Therefore, compared to Comparative Example 1, the batteries of Examples 1 to 14 are provided with a first positive electrode sheet. This first positive electrode sheet has a stable structure and can fully demonstrate the advantages of different positive electrode active materials. It can effectively mitigate the problems of impedance and current imbalance that occur between different types of positive electrode active materials in the composite cell, thereby improving the energy density and cycle performance of the battery. 【0105】 Comparing the performance test results corresponding to Example 1 and Comparative Example 2, as can be seen from Table 1, under the same conditions for other materials and operations used to prepare the batteries, the batteries prepared in Examples 1 to 14 have low impedance levels and superior energy density and cycle performance. In contrast, in Comparative Example 2, the mass ratio of the first positive electrode active material in the first positive electrode sheet exceeds the range of 10% to 50%, and the cycle performance of the battery obtained in this manner is clearly lower than that of the battery prepared in Example 1. From this, it can be seen that, compared to Comparative Example 2, the batteries according to Examples 1 to 14 are advantageous in that, by rationally setting the ratio of the first positive electrode active material in the first positive electrode sheet, the potential distribution of the first positive electrode sheet becomes uniform, and the lithium deposition phenomenon due to excessive local current density in the electrode sheet is mitigated, thereby improving the energy density and cycle performance of the battery. 【0106】 Comparing the performance test results corresponding to Example 1 with those of Comparative Examples 3-4, as can be seen from Table 1, under the same conditions for other materials and procedures used to prepare the batteries, the batteries prepared in Examples 1-14 had lower impedance levels and superior energy density and cycle performance. In contrast, the average single-sided surface density of the composite cathode active coating provided on the first cathode sheet prepared in Comparative Example 3 was <50 g / m². 2Therefore, the specific resistance is <0.0001 Ω / mm². 2 ·g, and the average single-sided surface density of the composite cathode active coating provided on the first cathode sheet prepared in Comparative Example 4 is >650 g / m². 2 Therefore, the specific resistance is >0.1500Ω / mm 2 ·g, and the cycle performance of the battery obtained in this way is clearly lower than that of the battery prepared in Example 1. From this, compared to Comparative Examples 3 to 4, the batteries according to Examples 1 to 12 are advantageous in that they make the potential distribution of the first positive electrode sheet uniform by rationally providing the surface density and specific surface resistance of the composite positive electrode active coating on the first positive electrode sheet, thereby mitigating the lithium deposition phenomenon caused by excessive local current density on the electrode sheet, and thereby improving the energy density and cycle performance of the battery. 【0107】 The performance test results of Example 1 and Examples 5-8 are compared. As can be seen from Table 1, under the same conditions for other materials and operations used to prepare the battery, the mass ratio of the first positive electrode active material to the total positive electrode active material in the composite cell was <5% and >40% in Examples 5 and 8, respectively. The cycle performance of the batteries obtained in this way is lower than that of the battery prepared in Example 1. From this, it can be seen that, compared to Examples 5 and 8, the composite cells of Examples 1, 6-7 are advantageous in improving the combined effect between different positive electrode active materials by rationally setting the content of the first positive electrode active material in the composite cell, achieving overall uniformity of current density in the composite cell, and improving the energy density and cycle performance of the battery by allowing positive electrode active materials with different energy densities to exert a synergistic advantage. 【0108】 The performance test results of Example 1 and Examples 9-12 are compared. As can be seen from Table 1, under the same conditions as other materials and operations for preparing the battery, the average surface density of the positive electrode active coating provided on the second positive electrode sheet in Example 9 is <65 g / m². 2 Therefore, the specific resistance is <0.0002Ω / mm². 2 ·g, and the average surface density of the positive electrode active coating provided on the second positive electrode sheet of Example 12 is >700g / m². 2 , specific surface resistance>0.2000Ω / mm2 ·g, and the cycle performance of the battery obtained in this way is lower than that of the battery prepared in Example 1. From this, compared to Examples 9 and 12, the composite cell according to Examples 1, 10-11 is superior in the combined effect of the second positive electrode sheet with the first positive electrode sheet by rationally setting the surface density and specific surface resistance of the second positive electrode sheet, exhibiting a synergistic advantage with the first positive electrode sheet, ensuring uniformity of current density between different positive electrode sheets, and avoiding phenomena such as destabilization of the electrode sheet structure, lithium deposition, and polarization due to poor combined effect of the electrode sheets, thereby improving the energy density and cycle performance of the battery. 【0109】 The above embodiments are used solely 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 they may modify or replace the technical solutions of the present invention in any equivalent manner, and that all such modifications or replacements will remain within the scope of protection of the present invention.

Claims

[Claim 1] It is a composite cell, The composite cell includes positive electrode sheets, the number of positive electrode sheets is greater than one, and each positive electrode sheet satisfies the condition that the ratio of its unit area capacity to the unit area capacity of any one other positive electrode sheet is between 0.9 and 1.

1. The positive electrode sheet includes a first positive electrode sheet, and the positive electrode active material contained in the first positive electrode sheet includes a first positive electrode active material and a second positive electrode active material, wherein the energy density of the first positive electrode active material is greater than the energy density of the second positive electrode active material. In each of the first positive electrode sheets, the mass of the first positive electrode active material is less than the mass of the second positive electrode active material, and the mass of the first positive electrode active material contained in the first positive electrode sheet is m1, and the total mass of the positive electrode active material contained in the first positive electrode sheet is m0. [Math 1] And, The number of layers of the positive electrode active coating provided on each of the first positive electrode sheets is greater than one, and the average single-sided surface density of the positive electrode active coating is 50 to 650 g / m². ２ The specific resistance is 0.0001 to 0.1500 Ω / mm². ２ A composite cell characterized in that the positive electrode active coating comprises a first positive electrode active coating and a second positive electrode active coating, the positive electrode active material contained in the first positive electrode active coating is composed of the first positive electrode active material, the positive electrode active material contained in the second positive electrode active coating is composed of the second positive electrode active material, and the positive electrode active coating formed of the first positive electrode active material and the positive electrode active coating formed of the second positive electrode active material are sequentially provided on the same side of the current collector of the first positive electrode sheet, along a direction away from the surface of the current collector. [Claim 2] The positive electrode sheet further comprises a second positive electrode sheet, and the average single-sided surface density of the positive electrode active coating provided on the second positive electrode sheet is 65 to 700 g / m². ２ The specific resistance is 0.0002 to 0.2000 Ω / mm². ２ The composite cell according to claim 1, characterized in that it is g. [Request Item 3] [Number 2] The composite cell according to feature 2. [Claim 4] The average single-sided surface density of the positive electrode active coating provided on the first positive electrode sheet is 100 to 500 g / m². ２ The specific resistance is 0.0001 to 0.1200 Ω / mm². ２ The composite cell according to claim 3, wherein it is g. [Claim 5] The average single-sided surface density of the positive electrode active coating provided on the second positive electrode sheet is 200 to 600 g / m². ２ The specific resistance is 0.0002 to 0.1600 Ω / mm². ２ The composite cell according to feature 4, wherein it is g. [Claim 6] In the composite cell, the total mass of the first positive electrode active material is M1, and the total mass of the positive electrode active material is M0. [Math 3] The composite cell according to feature 1. [Claim 7] The composite cell according to claim 1, characterized in that the first positive electrode active material is a ternary positive electrode material, and the second positive electrode active material comprises at least one of lithium iron phosphate, lithium iron manganese phosphate, and lithium manganate. [Claim 8] The composite cell according to claim 2, characterized in that the positive electrode active material used in the second positive electrode sheet contains one of lithium iron phosphate, lithium iron manganese phosphate, and lithium manganate. [Claim 9] A battery characterized by including a composite cell according to any one of claims 1 to 8.

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