Composite battery cell and battery comprising same

Abstract

A composite battery cell, comprising positive electrode sheets, wherein each positive electrode sheet satisfies the condition that the ratio of the capacity per unit area of the positive electrode sheet to the capacity per unit area of any other positive electrode sheet is 0.9-1.1. The positive electrode sheets include first positive electrode sheets, and positive electrode active materials contained in the first positive electrode sheet comprise 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 that of the second positive electrode active material. On each first positive electrode sheet, 10% ≤ (I) ≤ 50%, the average single side surface density of a positive electrode active coating layer is 50-650 g / m2, and the specific surface resistance is 0.0001-0.1500 Ω / mm2·g.

Description

Composite battery cell and battery containing same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 6, 2023, with application number 2023116748276. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the field of battery technology, and specifically relates to a composite battery cell and a battery containing the same. Background Art

[0003] Mainstream lithium-ion battery positive electrode materials mainly include oxide-based positive electrode active material systems and phosphate-based positive electrode active material systems. Oxide-based positive electrode active materials have high energy density but poor structural stability, while phosphate-based positive electrode active materials have low energy density but long cycle life and obvious cost and safety advantages. How to give full play to the complementary advantages of different materials has always been a difficult problem in the industry. At present, the industry generally adopts a blending method to directly coat the positive electrode slurry formed by mixing different types of positive electrode active materials on the surface of the current collector to prepare positive electrode sheets. However, the differences in particle size and surface energy of different types of positive electrode active materials cause the mixed slurry to agglomerate. The above problems can be avoided to a certain extent through multi-layer coating. However, when the proportions of different types of positive electrode active materials vary greatly, the coating surface density of the material with a smaller proportion is too small, and the coating process cannot be implemented. Technical issues

[0004] How to integrate different types of positive electrode sheets in the same battery cell and give full play to the synergistic advantages of different types of positive electrode active materials is a technical problem that technicians in this field urgently need to solve in their research.

[0005] Technical Solution

[0006] In a first aspect, the present application provides a composite battery cell, comprising a positive electrode sheet, wherein the number of positive electrode sheets is greater than 1, and each positive electrode sheet satisfies a ratio of its unit area capacity to the unit area capacity of any other positive electrode sheet of 0.9 to 1.1; the positive electrode sheet comprises a first positive electrode sheet, and the positive electrode active material contained in the first positive electrode sheet comprises 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; on each first positive electrode sheet, the mass of the first positive electrode active material is less than the mass of the second positive electrode active material, m1 represents the mass of the first positive electrode active material contained in the first positive electrode sheet, and m0 represents the total mass of the positive electrode active material contained in the first positive electrode sheet, On each first positive electrode sheet, the number of layers of the positive electrode active coating is greater than 1, and the average single-surface density of the positive electrode active coating is 50~650g / m 2, specific surface resistance is 0.0001~0.1500Ω / mm 2 g; The positive electrode active coating layer includes a first positive electrode active coating layer and a second positive electrode active coating layer, wherein the positive electrode active material contained in the first positive electrode active coating layer is composed of a first positive electrode active material, and the positive electrode active material contained in the second positive electrode active coating layer is composed of a second positive electrode active material.

[0007] In a second aspect, the present application provides a battery comprising the above-mentioned composite battery cell. Beneficial effects

[0008] The present application provides a composite battery cell and a battery containing the same, which fully utilizes the synergistic advantages of different types of positive electrode active materials and further improves the energy density, rate performance, and cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG1 is a schematic diagram of the structure of the composite battery cells in Examples 1 to 14 and Comparative Examples 2 to 4.

[0010] FIG2 is a schematic diagram of the structure of the composite battery cell in Comparative Example 1.

[0011] In the above drawings, the correspondence between the technical features and the drawing marks is: 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

[0012] In the composite battery cell provided in the present application, by regulating the proportion of the positive electrode active material in the first positive electrode sheet and the surface density and specific surface resistance of the first positive electrode sheet, it is beneficial to make the potential distribution of the first positive electrode sheet uniform, alleviate the lithium precipitation phenomenon caused by the excessive local current density of the electrode sheet, and at the same time help to improve the energy density of the electrode sheet. In addition, the capacity balance is basically achieved between the different positive electrode sheets in the composite battery cell, which further ensures the current density uniformity of the composite battery cell and reduces the impedance level of the electrode sheet. Based on this, the structure of the first positive electrode sheet provided in the present application is stable, which can give full play to the advantages of different positive electrode active materials, and effectively alleviate the impedance and current unevenness problems generated between different types of positive electrode active materials in the composite battery cell, so that the composite battery cell has excellent energy density, high and low temperature performance and cycle performance.

[0013] If the mass proportion of the first positive electrode active material is too small, the coating process accuracy will be limited, which may easily lead to processing problems. In addition, the lithium ion concentration and potential will be obviously unevenly distributed during high-rate charge and discharge, which may easily lead to lithium precipitation. If the mass proportion of the first positive electrode active material is too large, it will be detrimental to the structural stability of the first positive electrode sheet and the cost will be high.

[0014] If the surface density and specific surface resistance of the first positive electrode sheet are too large, the electron transmission path will be long and the transfer rate will be slow, which will reduce the electronic conductivity of the electrode sheet. In addition, the active material with a large volume effect will easily peel off from the current collector during the lithium insertion and extraction process, resulting in an unstable electrode structure. If the surface density and specific surface resistance of the first positive electrode sheet are too low, the coating accuracy of the electrode sheet will be limited, which will easily lead to processing problems and will be detrimental to the uniformity of the lithium ion insertion and extraction process, resulting in a decrease in the energy density of the battery cell.

[0015] Specifically, the average surface density of the positive electrode active coating provided on the positive electrode sheet is Di, the average gram capacity of the positive electrode active material contained in the positive electrode sheet is Ci, the average first efficiency of the positive electrode active material is Ei, the average mass proportion of the positive electrode active material is Wi, and its unit area capacity is .

[0016] 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.

[0017] In one embodiment, the positive electrode sheet further includes a second positive electrode sheet, and the average single-surface density of the positive electrode active coating provided on the second positive electrode sheet is 65-700 g / m 2 , specific surface resistance is 0.0002~0.2000Ω / mm 2 g. The second positive electrode sheet with a specific surface density and specific surface resistance is excellently matched with the first positive electrode sheet. The second positive electrode sheet can synergize with the first positive electrode sheet to ensure the uniformity of current density between different positive electrode sheets, avoid the phenomenon of unstable electrode structure, lithium deposition, polarization, etc. caused by poor electrode matching, thereby improving the energy density, high and low temperature performance, and cycle performance of the composite battery cell provided by the present application.

[0018] In one embodiment, .

[0019] In one embodiment, the average single-surface density of the positive electrode active coating provided on the first positive electrode sheet is 100-500 g / m 2 , specific surface resistance is 0.0001~0.1200Ω / mm 2 ·g.

[0020] In one embodiment, the average single-surface density of the positive electrode active coating provided on the second positive electrode sheet is 200-600 g / m 2 , specific surface resistance is 0.0002~0.1600Ω / mm 2 ·g.

[0021] In one embodiment, in the composite battery cell, the total mass of the first positive electrode active material is M1, the total mass of the positive electrode active material is M0, By rationally setting the content of the first positive electrode active material in the composite battery cell, it is beneficial to improve the matching effect between different positive electrode active materials, achieve uniformity of current density of the entire composite battery cell, and enable positive electrode active materials of different energy densities to play their synergistic advantages, thereby further improving the energy density and cycle performance of the battery.

[0022] In one embodiment, the first positive electrode active material is a ternary positive electrode material; and the second positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0023] In one embodiment, on the same side of the current collector of the first positive electrode sheet, the positive electrode active coating formed by the first active material and the positive electrode active coating formed by the second positive electrode active material are sequentially arranged in a direction away from the current collector surface.

[0024] In one embodiment, the positive electrode active material used in the second positive electrode sheet includes one of lithium iron phosphate, lithium manganese iron phosphate, and lithium manganese oxide.

[0025] In one embodiment, the composite battery 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, wherein 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.

[0026] Example 1

[0027] This embodiment provides a battery, and the preparation method thereof is as follows:

[0028] 1. Preparation of the second positive electrode sheet A 1-1

[0029] Lithium iron phosphate, binder PVDF, and conductive agent acetylene black were mixed uniformly in a mass ratio of 98:1:1 to prepare positive electrode slurry A. The positive electrode slurry A was applied on both sides of the positive electrode current collector and dried to form a positive electrode active coating A. The average single surface density of the positive electrode active coating A was S A 210g / m 2 The positive electrode sheet thus prepared is marked as the second positive electrode sheet A1-1; the specific surface resistance of the second positive electrode sheet A1-1 is 0.1230Ω / mm 2 g;

[0030] 2. Prepare the first positive electrode sheet D1 1-4

[0031] Lithium iron phosphate, binder PVDF, and conductive agent acetylene black are mixed uniformly in a mass ratio of 98:1:1 to form positive electrode slurry A; ternary positive electrode material, binder PVDF, and conductive agent acetylene black are mixed uniformly in a mass ratio of 90:5:5 to form positive electrode slurry C; then, the 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; then, the positive electrode slurry A 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 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 thus prepared is marked as the first positive electrode sheet D1 1-4. In the first positive electrode sheet D1 1-4, the average single-surface density S of the composite positive electrode active coating is 1. D1 165g / m 2 , specific surface resistance R D1 0.0500Ω / mm 2 g, and , wherein m1 represents the mass of the first positive electrode active material (ternary positive electrode material) contained in the first positive electrode sheet D1 1-4, and m0 represents the total mass of the positive electrode active material contained in the first positive electrode sheet D1 1-4.

[0032] 3. Preparation of composite battery cells

[0033] The structural diagram of the composite cell is shown in Figure 1. The composite cell is composed of a separator 1-2, a negative electrode sheet 1-3, a separator 1-2, a second positive electrode sheet A 1-1, a separator 1-2, a negative electrode sheet 1-3, a separator 1-2, a first positive electrode sheet D1 1-4, a separator 1-2, and a negative electrode sheet 1-3 stacked in sequence (wherein, there are 6 second positive electrode sheets A 1-1 and 44 first positive electrode sheets D1 1-4). The composite cell meets the following requirements: , where M1 represents the mass of the first positive electrode active material (ternary positive electrode material) in the composite battery cell, and M0 represents the total mass of all positive electrode active materials in the composite battery cell; and the composite battery cell 1 satisfies: ;Q D1 represents the capacity per unit area of ​​the first positive electrode sheet D1 1-4, Q A It represents the capacity per unit area of ​​the second positive electrode sheet A1-1.

[0034] 4. Prepare the battery

[0035] The composite battery cell is placed in a battery shell, and then the battery shell is subjected to treatments such as welding the tabs and baking. After the moisture content is tested to be qualified, an appropriate amount of electrolyte is injected into the battery shell, and the battery is packaged. The battery is prepared through aging, formation, and vacuum packaging.

[0036] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0037] Example 2

[0038] This embodiment provides a battery, and the preparation method thereof is as follows:

[0039] 1. Preparation of the second positive electrode sheet B 1-1

[0040] Lithium manganese iron phosphate, binder PVDF, and conductive agent acetylene black were mixed uniformly in a mass ratio of 98:1:1 to prepare a positive electrode slurry B. The positive electrode slurry B was applied on both sides of the positive electrode current collector and dried to form a positive electrode active coating B. The average single surface density of the positive electrode active coating B was S B 175g / m 2 The positive electrode sheet thus prepared is marked as the second positive electrode sheet B1-1; the specific surface resistance R B 0.1230Ω / mm 2 g;

[0041] 2. Prepare the first positive electrode sheet D2 1-4

[0042] Lithium manganese iron phosphate, binder PVDF, and conductive agent acetylene black are mixed uniformly in a mass ratio of 98:1:1 to form a positive electrode slurry B; ternary positive electrode material, binder PVDF, and conductive agent acetylene black are mixed uniformly in a mass ratio of 90:5:5 to form a positive electrode slurry C; then, the 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; then, the positive electrode slurry B 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 D2 1-4. The first positive electrode sheet thus prepared is marked as the first positive electrode sheet D2 1-4. In the first positive electrode sheet D2 1-4, the average single-surface density S of the composite positive electrode active coating is 1. D2 160g / m 2 , specific surface resistance R D1 0.0800Ω / mm 2 g, and , wherein m1 represents the mass of the first positive electrode active material (ternary positive electrode material) contained in the first positive electrode sheet D2 1-4, and m0 represents the total mass of the positive electrode active material contained in the first positive electrode sheet D2 1-4.

[0043] 3. Preparation of composite battery cells

[0044] The structural diagram of the composite cell is shown in Figure 1. The composite cell is composed of a separator 1-2, a negative electrode sheet 1-3, a separator 1-2, a second positive electrode sheet B 1-1, a separator 1-2, a negative electrode sheet 1-3, a separator 1-2, a first positive electrode sheet D2 1-4, a separator 1-2, and a negative electrode sheet 1-3 stacked in sequence (wherein, there are 6 second positive electrode sheets B 1-1 and 44 first positive electrode sheets D2 1-4). The composite cell meets the following requirements: , where M1 represents the mass of the first positive electrode active material (ternary positive electrode material) in the composite battery cell, and M0 represents the total mass of all positive electrode active materials in the composite battery cell; and the composite battery cell satisfies: ;Q D2 represents the capacity per unit area of ​​the first positive electrode sheet D2 1-4, Q B It represents the capacity per unit area of ​​the second positive electrode sheet B1-1.

[0045] 4. Prepare the battery

[0046] The composite battery cell is placed in a battery shell, and then the battery shell is subjected to treatments such as welding the tabs and baking. After the moisture content is tested to be qualified, an appropriate amount of electrolyte is injected into the battery shell, and the battery is packaged. The battery is prepared through aging, formation, and vacuum packaging.

[0047] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0048] Example 3

[0049] This embodiment provides a battery, and the preparation method thereof is as follows:

[0050] 1. Preparation of the second positive electrode sheet A 1-1

[0051] The preparation method of the second positive electrode sheet A is similar to that of the second positive electrode sheet A in Example 1;

[0052] 2. Prepare the first positive electrode sheet D2 1-4

[0053] The preparation method of the first positive electrode sheet D2 refers to the preparation method of the first positive electrode sheet D2 in Example 2.

[0054] 3. Preparation of composite battery cells

[0055] The structural diagram of the composite cell is shown in Figure 1. The composite cell is composed of a separator 1-2, a negative electrode sheet 1-3, a separator 1-2, a second positive electrode sheet A 1-1, a separator 1-2, a negative electrode sheet 1-3, a separator 1-2, a first positive electrode sheet D2 1-4, a separator 1-2, and a negative electrode sheet 1-3 stacked in sequence (wherein, there are 6 second positive electrode sheets A 1-3 and 44 first positive electrode sheets D2 1-4). The composite cell meets the following requirements: , where M1 represents the mass of the first positive electrode active material (ternary positive electrode material) in the composite battery cell, and M0 represents the total mass of all positive electrode active materials in the composite battery cell; ;Q D2 represents the capacity per unit area of ​​the first positive electrode sheet D2 1-4, Q A It represents the capacity per unit area of ​​the second positive electrode sheet A1-1.

[0056] 4. Prepare the battery

[0057] The composite battery cell is placed in a battery shell, and then the battery shell is subjected to treatments such as welding the tabs and baking. After the moisture content is tested to be qualified, an appropriate amount of electrolyte is injected into the battery shell, and the battery is packaged. The battery is prepared through aging, formation, and vacuum packaging.

[0058] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0059] Example 4

[0060] This embodiment provides a battery, and the preparation method thereof is as follows:

[0061] 1. Preparation of the second positive electrode sheet A 1-1

[0062] The preparation method of the second positive electrode sheet A is similar to that of the second positive electrode sheet A in Example 1;

[0063] 2. Preparation of the first positive electrode sheet D3 1-4

[0064] The ternary positive electrode material, the binder PVDF, and the conductive agent acetylene black are mixed uniformly in a mass ratio of 90:5:5 to form a positive electrode slurry C; lithium manganese oxide, the binder PVDF, and the conductive agent acetylene black are mixed uniformly in a mass ratio of 94:3:3 to form a positive electrode slurry D; then, the 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. Then, the 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. The first positive electrode sheet thus prepared is marked as the first positive electrode sheet D3 1-4. In the first positive electrode sheet D3 1-4, the average single-surface density S of the composite positive electrode active coating is 1. D3 175g / m 2 , specific surface resistance R D1 0.1000Ω / mm 2 g, and , wherein m1 represents the mass of the first positive electrode active material (ternary positive electrode material) contained in the first positive electrode sheet D3 1-4, and m0 represents the total mass of the positive electrode active material contained in the first positive electrode sheet D3 1-4.

[0065] 3. Preparation of composite battery cells

[0066] The structural diagram of the composite cell is shown in Figure 1. The composite cell is composed of a separator 1-2, a negative electrode sheet 1-3, a separator 1-2, a second positive electrode sheet A 1-1, a separator 1-2, a negative electrode sheet 1-3, a separator 1-2, a first positive electrode sheet D3 1-4, a separator 1-2, and a negative electrode sheet 1-3 stacked in sequence (wherein, there are 6 second positive electrode sheets A 1-1 and 44 first positive electrode sheets D3 1-4). The composite cell meets the following requirements: , M1 represents the total mass of a few positive electrode active materials (ternary positive electrode materials) in the composite battery cell, and M0 represents the total mass of all positive electrode active materials in the composite battery cell; and the composite battery cell satisfies: ;Q D3 represents the capacity per unit area of ​​the first positive electrode sheet D3 1-4, Q A It represents the capacity per unit area of ​​the second positive electrode sheet A1-1.

[0067] 4. Prepare the battery

[0068] The composite battery cell is placed in a battery shell, and then the battery shell is subjected to treatments such as welding the tabs and baking. After the moisture content is tested to be qualified, an appropriate amount of electrolyte is injected into the battery shell, and the battery is packaged. The battery is prepared through aging, formation, and vacuum packaging.

[0069] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0070] Example 5

[0071] This embodiment prepares a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that: in the first positive electrode sheet D1 1-4, In composite cells, Except for the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0072] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0073] Example 6

[0074] This embodiment prepares a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that: in the first positive electrode sheet D1 1-4, In composite cells, =5%. Except for the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0075] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0076] Example 7

[0077] This embodiment prepares a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that: in the first positive electrode sheet D1 1-4, =10%; in composite cells, =40%. Except for the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0078] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0079] Example 8

[0080] This embodiment prepares a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that: in the first positive electrode sheet D1 1-4, =10%; in composite cells, =42%. Except for the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0081] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0082] Example 9

[0083] This embodiment is used to prepare a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that in the second positive electrode sheet A1-1, the average single surface density of the positive electrode active coating A is 50 g / m 2 , the specific surface resistance is 0.0001Ω / mm 2 g. Except for the above differences, the materials and process operations used in this example are strictly consistent with those in Example 1.

[0084] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0085] Example 10

[0086] This embodiment is used to prepare a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that in the second positive electrode sheet A1-1, the average single surface density of the positive electrode active coating A is 65 g / m 2 , the specific surface resistance is 0.0002Ω / mm 2g. Except for the above differences, the materials and process operations used in this example are strictly consistent with those in Example 1.

[0087] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0088] Example 11

[0089] This embodiment is a battery prepared with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that in the second positive electrode sheet A1-1, the average single surface density of the positive electrode active coating A is 700 g / m 2 , the specific surface resistance is 0.2Ω / mm 2 g. Except for the above differences, the materials and process operations used in this example are strictly consistent with those in Example 1.

[0090] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0091] Example 12

[0092] This embodiment is used to prepare a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that in the second positive electrode sheet A1-1, the average single surface density of the positive electrode active coating A is 750 g / m 2 , the specific surface resistance is 0.25Ω / mm 2 g. Except for the above differences, the materials and process operations used in this example are strictly consistent with those in Example 1.

[0093] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0094] Example 13

[0095] This embodiment is used to prepare a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that in the first positive electrode sheet D1 1-4, the surface density S of the composite positive electrode active coating is D1 650g / m 2 , specific surface resistance R D1 0.0001Ω / mm 2 g. Except for the above differences, the materials and process operations used in this example are strictly consistent with those in Example 1.

[0096] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0097] Example 14

[0098] This embodiment is used to prepare a battery with reference to the embodiment 1. The difference between this embodiment and the embodiment 1 is that in the first positive electrode sheet D1 1-4, the surface density S of the composite positive electrode active coating isD1 50g / m 2 , specific surface resistance R D1 0.0500Ω / mm 2 ·g

[0099] Except for the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0100] The structural schematic diagram of the composite battery cell prepared in this embodiment is shown in FIG1 .

[0101] Comparative Example 1

[0102] This comparative example provides a battery, and its preparation method is as follows:

[0103] 1. Preparation of the second positive electrode sheet B 2-1

[0104] Lithium manganese iron phosphate, binder PVDF, and conductive agent acetylene black were mixed uniformly in a mass ratio of 98:1:1 to prepare a positive electrode slurry B. The positive electrode slurry B was applied on both sides of the positive electrode current collector and dried to form a positive electrode active coating B. The average single surface density of the positive electrode active coating B was S B 175g / m 2 , specific surface resistance is 0.1200Ω / mm 2 g. The positive electrode sheet thus prepared is marked as the second positive electrode sheet B 2-1;

[0105] 2. Preparation of the second positive electrode sheet C 2-4

[0106] The ternary material, binder PVDF, and conductive agent acetylene black were mixed uniformly in a mass ratio of 90:5:5 to prepare a positive electrode slurry C. The positive electrode slurry C was applied on both sides of the positive electrode current collector and dried to form a positive electrode active coating C. The average single surface density of the positive electrode active coating C was S C 150g / m 2 , the specific surface resistance is 0.1250Ω / mm 2 g. The positive electrode sheet thus prepared is marked as the second positive electrode sheet C 2-4;

[0107] 3. Preparation of composite battery cells

[0108] The structural diagram of the composite cell is shown in Figure 2. The composite cell is composed of a separator 2-2, a negative electrode sheet 2-3, a second positive electrode sheet B 2-1, a separator 2-2, a negative electrode sheet 2-3, a separator 2-2, a second positive electrode sheet C 2-4, a separator 2-2, and a negative electrode sheet 2-3 stacked in sequence (wherein, there are 44 second positive electrode sheets B 2-1 and 6 second positive electrode sheets C 2-4); and the composite cell 1 meets the following requirements: =1.05;Q Crepresents the capacity per unit area of ​​the second positive electrode sheet C 2-4, Q B It represents the capacity per unit area of ​​the second positive electrode sheet B2-1.

[0109] 4. Prepare the battery

[0110] The composite battery cell is placed in a battery shell, and then the battery shell is subjected to treatments such as welding the tabs and baking. After the moisture content is tested to be qualified, an appropriate amount of electrolyte is injected into the battery shell, and the battery is packaged. The battery is prepared through aging, formation, and vacuum packaging.

[0111] The structural diagram of the composite battery cell prepared in this comparative example is shown in FIG2 .

[0112] Comparative Example 2

[0113] This comparative example is used to prepare a battery with reference to Example 1. The difference between this comparative example and Example 1 is that: in the first positive electrode sheet D1 1-4, =7.5%, in composite cells, =10%. Except for the above differences, the materials and process operations used in this comparative example are strictly consistent with those of Comparative Example 1.

[0114] The structural diagram of the composite battery cell prepared in this comparative example is shown in FIG1 .

[0115] Comparative Example 3

[0116] This comparative example is used to prepare a battery with reference to Example 1. The difference between this comparative example and Example 1 is that in the first positive electrode sheets D1 1-4, the average single surface density S of the composite positive electrode active coating is D1 30g / m 2 , specific surface resistance R D1 0.00007Ω / mm 2 g. Except for the above differences, the materials and process operations used in this comparative example are strictly consistent with those of Comparative Example 1.

[0117] The structural diagram of the composite battery cell prepared in this comparative example is shown in FIG1 .

[0118] Comparative Example 4

[0119] This comparative example is used to prepare a battery with reference to Example 1. The difference between this comparative example and Example 1 is that in the first positive electrode sheet D1 1-4, the surface density S of the composite positive electrode active coating is D1 700g / m 2 , specific surface resistance R D1 0.20Ω / mm 2 g. Except for the above differences, the materials and process operations used in this comparative example are strictly consistent with those of Comparative Example 1.

[0120] The structural diagram of the composite battery cell prepared in this comparative example is shown in FIG1 .

[0121] Test Case

[0122] 1. Participants

[0123] This test example uses the batteries prepared in Examples 1 to 14 and Comparative Examples 1 to 4 as test objects.

[0124] 2. Test content

[0125] (1) Energy density

[0126] The battery under test was operated at a constant current and constant voltage of 0.33C.

[0127] Charge to 4.25V, cut off at 0.02C, then discharge to 2.8V at 0.33C, record the capacity, average voltage and cell mass, and calculate the energy density of the battery according to the following formula: Energy density = capacity * average voltage / battery mass.

[0128] (2) DC impedance

[0129] The test battery was charged at a constant current and constant voltage of 0.33C to 4.25V, cut off at 0.02C, then discharged at 0.33C for 90min, left for 10min, and the terminal voltage V1 was recorded; then discharged at 2C (current I) for 10s, and the terminal voltage V2 was recorded. The DC impedance of the sodium ion battery was calculated according to the following formula: DC impedance = |V1-V2| / I.

[0130] (3) Cycle performance

[0131] The test battery was placed in a constant temperature box at 45℃, charged at a constant current and constant voltage of 1C, cut off at 0.02C, and then discharged at 1C, cycled to 80% SOC, and the number of cycles was recorded.

[0132] 3. Test results

[0133] Table 1. Battery parameters for this test case

[0134]

[0135] Table 2. Battery performance test results of this test case

[0136] Group Energy density (Wh / kg) DC impedance (mΩ) Cycle number (turns) Example 1 250 2.0 1750 Example 2 250 2.0 1800 Example 3 250 1.9 1780 Example 4 245 2.1 1600 Example 5 245 2.5 1500 Example 6 245 2.2 1700 Example 7 245 2.1 1750 Example 8 245 2.5 1450 Example 9 245 2.41600 Example 10 250 2.11700 Example 11 250 2.11680 Example 12 245 2.31650 Example 13 250 2.11700 Example 14 250 2.11680 Comparative Example 1 250 2.81300 Comparative Example 2 235 2.91250 Comparative Example 3 235 2.91260 Comparative Example 4 235 2.91200

[0137] The relevant performance test results of the batteries prepared in Examples 1 to 14 and Comparative Examples 1 to 4 are shown in Table 1.

[0138] Comparing the performance test results corresponding to Example 1 and Comparative Example 1, it can be seen from Table 1 that, under the same conditions for other materials and operations in preparing the batteries, the batteries prepared in Examples 1 to 14 have low impedance levels and excellent energy density and cycle performance. However, the composite battery cell prepared in Comparative Example 1, in which only the second positive electrode sheet is provided, has a battery cycle performance significantly lower than that of the battery prepared in Example 1. This shows that, compared to Comparative Example 1, the batteries provided in Examples 1 to 14 are provided with a first positive electrode sheet. This first positive electrode sheet has a stable structure and can fully utilize the advantages of different positive electrode active materials, effectively alleviating the impedance and current imbalance problems caused by different types of positive electrode active materials in the composite battery cell, thereby improving the energy density and cycle performance of the battery.

[0139] Comparing the performance test results corresponding to Example 1 and Comparative Example 2, it can be seen from Table 1 that, under the same conditions for preparing other materials and operations, the batteries prepared in Examples 1 to 14 have low impedance levels and excellent energy density and cycle performance. However, in the first positive electrode sheet prepared in Comparative Example 2, the mass proportion of the first positive electrode active material exceeds the range of 10% to 50%, and the cycle performance of the resulting battery is significantly lower than that of the battery prepared in Example 1. This shows that, compared with Comparative Example 2, the batteries provided by Examples 1 to 14, by reasonably setting the mass proportion of the first positive electrode active material in the first positive electrode sheet, are conducive to uniform potential distribution of the first positive electrode sheet, alleviate lithium plating caused by excessive local current density in the electrode sheet, and thus improve the energy density and cycle performance of the battery.

[0140] Comparing the performance test results of Example 1 with those of Comparative Examples 3-4, it can be seen from Table 1 that, under the same conditions of other materials and operations for preparing the batteries, the batteries prepared in Examples 1-14 have low impedance levels, and excellent energy density and cycle performance, while the average single-surface density of the composite positive electrode active coating provided on the first positive electrode sheet prepared in Comparative Example 3 is less than 50 g / m 2 , specific surface resistance <0.0001Ω / mm 2 ·g, the average single-surface density of the composite positive electrode active coating provided on the first positive electrode sheet prepared in Comparative Example 4 is greater than 650g / m 2 , specific surface resistance>0.1500Ω / mm 2 g, and the cycle performance of the battery obtained thereby is significantly lower than that of the battery prepared in Example 1. This indicates that, compared with Comparative Examples 3-4, the batteries provided in Examples 1-12, by rationally setting the surface density and specific surface resistance of the composite positive electrode active coating in the first positive electrode sheet, are conducive to uniform potential distribution of the first positive electrode sheet, alleviating lithium plating caused by excessive local current density in the electrode sheet, thereby improving the energy density and cycle performance of the battery.

[0141] The performance test results of Example 1 were compared with those of Examples 5 to 8. As shown in Table 1, under the same conditions for preparing other materials and operations for the battery, the mass proportion of the first positive electrode active material in the composite battery cell in Examples 5 and 8 was less than 5% and greater than 40%, respectively, and the cycle performance of the resulting batteries was lower than that of the battery prepared in Example 1. This shows that, compared with Examples 5 and 8, the composite battery cells provided by Examples 1, 6 to 7, by reasonably setting the content of the first positive electrode active material in the composite battery cell, are conducive to improving the matching effect between different positive electrode active materials, achieving uniformity of current density of the entire composite battery cell, and allowing positive electrode active materials of different energy densities to exert their synergistic advantages, thereby improving the energy density and cycle performance of the battery.

[0142] The performance test results of Example 1 were compared with those of Examples 9 to 12. As shown in Table 1, under the same conditions of other materials and operations for preparing the battery, the average surface density of the positive electrode active coating on the second positive electrode sheet in Example 9 was less than 65 g / m 2 , specific surface resistance <0.0002Ω / mm 2 g, the average surface density of the positive electrode active coating provided on the second positive electrode sheet of Example 12 is greater than 700 g / m 2 , specific surface resistance>0.2000Ω / mm 2g, and the cycle performance of the battery obtained thereby is lower than that of the battery prepared in Example 1. This shows that, compared with Examples 9 and 12, the composite battery cells provided by Examples 1, 10-11 have an excellent matching effect with the first positive electrode sheet by reasonably setting the surface density and specific surface resistance of the second positive electrode sheet. The second positive electrode sheet with a specific surface density and specific surface resistance can play a synergistic role with the first positive electrode sheet, ensure the uniformity of current density between different positive electrode sheets, avoid the phenomenon of unstable electrode structure, lithium deposition, polarization, etc. caused by poor electrode sheet matching, and thus improve the energy density and cycle performance of the battery.

Claims

1. [Corrected according to Rule 26 on 04.01.2024] A composite battery cell, The composite battery cell includes positive electrode sheets, the number of the positive electrode sheets is greater than 1, and each positive electrode sheet satisfies that the ratio of its unit area capacity to the unit area capacity of any other positive electrode sheet is 0.9 to 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; On 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. Let m1 represent the mass of the first positive electrode active material contained in the first positive electrode sheet, and let m0 represent the total mass of the positive electrode active material contained in the first positive electrode sheet. On each of the first positive electrode sheets, the number of layers of the positive electrode active coating provided is greater than 1, and the average single-sided surface density of the positive electrode active coating is 50 to 650 g / m 2 , and the specific surface resistance is 0.0001 to 0.1500 Ω / mm 2 ·g; the positive electrode active coating includes 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.

2. The composite battery cell according to claim 1, wherein, 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.

3. [Corrected according to Rule 26 on 04.01.2024] The composite battery cell according to claim 2, wherein, 4. The composite battery cell according to claim 3, wherein, The average single-sided areal 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.

5. The composite battery cell according to claim 4, wherein, The average single-sided areal density of the positive electrode active coating provided on the second positive electrode sheet is 200~600 g / m 2 , and the specific surface resistance is 0.0002~0.1600 Ω / mm 2 ·g.

6. [Corrected according to Rule 26 on 04.01.2024] The composite battery cell according to claim 1, wherein, In the composite battery 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.

7. The composite battery cell according to claim 1, wherein, The first positive electrode active material is a ternary positive electrode material, and the second positive electrode active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, and lithium manganate.

8. The composite battery cell according to claim 7, wherein, On the same side of the current collector of the first positive electrode sheet, in the direction away from the surface of the current collector, the positive electrode active coating formed by the first active material and the positive electrode active coating formed by the second positive electrode active material are arranged in sequence.

9. The composite battery cell according to claim 2, wherein, The positive electrode active material used for the second positive electrode sheet includes one of lithium iron phosphate, lithium iron manganese phosphate, and lithium manganate.

10. A battery, comprising the composite battery cell according to any one of claims 1 to 9.

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