Positive electrode sheet and battery

Abstract

The application provides a positive plate and a battery, wherein the positive plate comprises a current collector, a surface of the current collector comprises a first region, a second region and a third region, the first region and the third region are respectively located on two sides of the second region, the first region of the current collector is coated with a first coating layer, the second region of the current collector is coated with a second coating layer, and the third region of the current collector is coated with a third coating layer, and the delithiation capacity of the first coating layer and the third coating layer is greater than that of the second coating layer. The positive plate provided in the application embodiment alleviates the problem of lithium precipitation in the edge regions of the negative plate.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a positive electrode and a battery. Background Technology

[0002] With the rapid development of lithium-ion battery technology, lithium-ion batteries are being used more and more widely in portable mobile electronic devices such as laptops and smartphones.

[0003] Currently, during high-current fast charging of batteries, there is a concentration difference in lithium salt concentration between the edges of the positive and negative electrodes and the middle region between the positive and negative electrodes. In the edge regions of the positive and negative electrodes, the lithium salt concentration in the electrolyte is lower, which leads to overpotential in the negative electrode edge region, resulting in severe lithium deposition on both sides of the negative electrode edge. Summary of the Invention

[0004] This application provides a positive electrode and a battery that alleviates the problem of lithium plating in the edge regions on both sides of the negative electrode.

[0005] To achieve the above objectives, in a first aspect, embodiments of this application provide a positive electrode sheet, including a current collector. The surface of the current collector includes a first region, a second region, and a third region. The first region and the third region are respectively located on both sides of the second region. The first region of the current collector is coated with a first coating, the second region of the current collector is coated with a second coating, and the third region of the current collector is coated with a third coating. The delithiation capabilities of the first coating and the third coating are both greater than the delithiation capability of the second coating.

[0006] Optionally, the delithiation capability of the first coating is the same as that of the third coating.

[0007] Optionally, the delithiation capacity of the active material in the first coating and the third coating is greater than that of the active material in the second coating.

[0008] Optionally, the active material in the first coating and the third coating is a high-nickel ternary material, and the active material in the second coating includes at least one of medium-nickel ternary materials, low-nickel ternary materials, lithium cobalt oxide, and lithium iron phosphate.

[0009] Alternatively, the active material in the first coating and the third coating is a medium-nickel ternary material, and the active material in the second coating includes at least one of low-nickel ternary materials, lithium cobalt oxide, and lithium iron phosphate;

[0010] Alternatively, the active material in the first coating and the third coating may be lithium cobalt oxide, and the active material in the second coating may be lithium iron phosphate.

[0011] Optionally, the mass percentage of active material in the first coating and the mass percentage of active material in the third coating are both greater than the mass percentage of active material in the second coating.

[0012] Optionally, the mass percentage of active material in the first coating and the mass percentage of active material in the third coating are both in the range of 98.5% to 97%.

[0013] The mass percentage of the active material in the second coating ranges from 96% to 95%.

[0014] Optionally, the thickness of both the first coating and the third coating is greater than the thickness of the second coating.

[0015] Optionally, the active materials in the first coating, the second coating, and the third coating all have the same delithiation capability.

[0016] Optionally, the widths of the first region and the third region in the positive electrode width direction are both less than or equal to 0.05 times the width of the second region in the positive electrode width direction.

[0017] Secondly, embodiments of this application provide a battery including a negative electrode, an electrolyte, and a positive electrode as described in the first aspect, wherein the negative electrode and the positive electrode are disposed opposite to each other, and both the negative electrode and the positive electrode are placed in the electrolyte.

[0018] In this embodiment, by making the delithiation capacity of the coatings (i.e., the first coating and the third coating) at the edge of the current collector of the positive electrode greater than that of the coatings (i.e., the second coating) in the middle of the current collector of the positive electrode greater, more lithium ions can be deposited at the edge of the positive electrode, thereby increasing the lithium salt concentration of the electrolyte at the edge of both the positive and negative electrodes, avoiding overpotential at the edge of the negative electrode, and thus alleviating the problem of lithium deposition at the edge of both sides of the negative electrode. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings are described below. Obviously, the following drawings are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the listed drawings without creative effort.

[0020] Figure 1 This is one of the structural schematic diagrams of the positive electrode sheet provided in the embodiments of this application;

[0021] Figure 2 This is the second schematic diagram of the positive electrode sheet provided in the embodiments of this application;

[0022] Figure 3This is a schematic diagram of the negative electrode sheet provided in the embodiments of this application. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0024] See Figure 1 and Figure 2 This application provides a positive electrode sheet, including a current collector 10. The surface of the current collector 10 includes a first region, a second region, and a third region. The first region and the third region are located on both sides of the second region. The first region of the current collector 10 is coated with a first coating 11, the second region of the current collector 10 is coated with a second coating 12, and the third region of the current collector 10 is coated with a third coating 13. The delithiation capabilities of the first coating 11 and the third coating 13 are both greater than the delithiation capability of the second coating 12.

[0025] In practice, the delithiation capabilities of the first coating 11 and the third coating 13 may be different. For example, the delithiation capability of the first coating 11 may be greater than that of the third coating 13, or the delithiation capability of the first coating 11 may be less than that of the third coating 13.

[0026] When the delithiation capabilities of the first coating 11 and the third coating 13 are different, the lithium salt concentration of the electrolyte at the two edge regions of the positive and negative electrodes will be different, which may lead to uneven lithium deposition at the two edge regions of the negative electrode. In order to make the lithium deposition at the two edge regions of the negative electrode uniform and improve the battery life, in an optional embodiment of this application, the delithiation capabilities of the first coating 11 and the third coating 13 are the same.

[0027] The shapes of the first and third regions include, but are not limited to, rectangles, triangles, trapezoids, and irregular shapes. The first, second, and third regions may completely cover the surface of the current collector 10 of the positive electrode sheet, or they may not completely cover the surface of the current collector 10 of the positive electrode sheet. To make the positive electrode sheet relatively flat overall, thereby improving the battery's lifespan and safety performance, in an optional embodiment of this application, the first, second, and third regions are adjacent to each other.

[0028] In this embodiment, by making the delithiation capacity of the coatings (i.e., the first coating 11 and the third coating 13) at the edge of the current collector 10 of the positive electrode greater than that of the coatings (i.e., the second coating 12) in the middle region of the current collector 10 of the positive electrode greater, more lithium ions can be deposited at the edge of the positive electrode, thereby increasing the lithium salt concentration of the electrolyte at the edge of both the positive and negative electrodes, avoiding overpotential at the edge of the negative electrode, and thus alleviating the problem of lithium deposition at the edge of both sides of the negative electrode.

[0029] The embodiments of this application provide at least the following methods for achieving a greater delithiation capability of the first coating 11 and the third coating 13 than that of the second coating 12.

[0030] Method 1: The delithiation capacity of the active material in the first coating 11 and the third coating 13 is greater than that of the active material in the second coating 12.

[0031] Method 2: The delithiation capacity of the active material in the first coating 11 and the third coating 13 is equal to that of the active material in the second coating 12. The thickness of the first coating 11 and the third coating 13 is equal to that of the second coating 12. Furthermore, the mass percentage of the active material in the first coating 11 and the mass percentage of the active material in the third coating 13 are both greater than the mass percentage of the active material in the second coating 12.

[0032] Method 3: The delithiation capacity of the active material in the first coating 11 and the third coating 13 is equal to that of the active material in the second coating 12. The mass ratio of the active material in the first coating 11 and the mass ratio of the active material in the third coating 13 are equal to that of the active material in the second coating 12. Furthermore, the thickness of the first coating 11 and the third coating 13 is greater than that of the second coating 12.

[0033] Method 4: The delithiation capacity of the active material in the first coating 11 and the third coating 13 is equal to that of the active material in the second coating 12. The mass ratio of the active material in the first coating 11 and the third coating 13 is greater than that of the active material in the second coating 12. The thickness of the first coating 11 and the third coating 13 is greater than that of the second coating 12.

[0034] It should be noted that, in Method 1, the mass percentage of active material in the first coating 11 and the mass percentage of active material in the third coating 13 can both be equal to the mass percentage of active material in the second coating 12, and the mass percentage of active material in the first coating 11 and the mass percentage of active material in the third coating 13 can both be greater than the mass percentage of active material in the second coating 12.

[0035] Similarly, in Method 1, the thickness of the first coating 11 and the third coating 13 can be equal to the thickness of the second coating 12, or the thickness of the first coating 11 and the third coating 13 can be greater than the thickness of the second coating 12.

[0036] In methods two, three, and four, by making the delithiation capabilities of the active materials in the first coating 11 and the third coating 13 equal to those in the second coating 12, the active materials in the first coating 11, the second coating 12, and the third coating 13 can be identical. This simplifies the manufacturing process of the positive electrode sheet, thereby reducing production costs.

[0037] Optionally, the delithiation capabilities of the active materials in the first coating 11 and the third coating 13 are both greater than those of the active materials in the second coating 12. This is the method described above. In this method, different active materials can be selected to achieve a greater delithiation capability of the active materials in the first coating 11 and the third coating 13 than that in the second coating 12, making the implementation relatively simple.

[0038] Optionally, the active material in the first coating 11 and the third coating 13 is a high-nickel ternary material Ni. 0.8 Co 0.1 Mn 0.1 The active material in the second coating 12 includes a medium-nickel ternary material Ni. 0.6 Co 0.1 Mn 0.4 Low-nickel ternary materials Ni 0.5 Co 0.3 Mn 0.2 At least one of lithium cobalt oxide (LiCoO2) and lithium iron phosphate (LiFePO4);

[0039] Alternatively, the active material in the first coating 11 and the third coating 13 is a medium-nickel ternary material, and the active material in the second coating 12 includes at least one of low-nickel ternary material, lithium cobalt oxide, and lithium iron phosphate.

[0040] Alternatively, the active material in the first coating 11 and the third coating 13 is lithium cobalt oxide, and the active material in the second coating 12 is lithium iron phosphate.

[0041] By ensuring that the active materials in the first coating 11, the second coating 12, and the third coating 13 meet the above-mentioned requirements, the delithiation capacity of the active materials in the first coating 11 and the third coating 13 can be greater than that of the active materials in the second coating 12.

[0042] Optionally, the mass percentage of active material in the first coating 11 and the mass percentage of active material in the third coating 13 are both greater than the mass percentage of active material in the second coating 12.

[0043] The percentage of active material in the first coating 11 refers to the ratio of the total mass of active material in the first coating 11 to the total mass of the first coating 11.

[0044] The percentage of active material in the second coating 12 refers to the ratio of the total mass of active material in the second coating 12 to the total mass of the second coating 12.

[0045] The percentage of active material in the third coating 13 refers to the ratio of the total mass of active material in the third coating 13 to the total mass of the third coating 13.

[0046] In practice, the mass percentage of active material in both the first coating 11 and the third coating 13 ranges from 98.5% to 97%. For example, the mass percentages of active material in the first coating 11 and the third coating 13 can be any one of 98.5%, 98.2%, 98%, 97.8%, 97.5%, 97.2%, or 97%. The mass percentages of active material in the first coating 11 and the third coating 13 can be the same or different. When the mass percentages of active material in the first coating 11 and the third coating 13 are the same, the manufacturing process of the positive electrode sheet can be simplified, thereby reducing production costs.

[0047] The mass percentage of the active material in the second coating 12 ranges from 96% to 95%. For example, the mass percentage of the active material in the second coating 12 can be any one of 96%, 95.8%, 95.5%, 95.2%, or 95%.

[0048] Optionally, the thickness of the first coating 11 and the third coating 13 is greater than the thickness of the second coating 12.

[0049] In practice, the thicknesses of the first coating 11 and the third coating 13 can be different. In order to make the positive electrode sheet more flat overall, thereby improving the battery's lifespan and safety performance, the thicknesses of the first coating 11 and the third coating 13 can also be the same.

[0050] To further improve the overall flatness of the positive electrode sheet, thereby enhancing the battery's lifespan and safety performance, the first coating 11 and the third coating 13 have the same thickness, and the thickness difference between the first coating 11 and the second coating 12 ranges from greater than 5 micrometers to less than 10 micrometers. Specifically, the thickness difference between the first coating 11 and the second coating 12 is any one of 5.5 micrometers, 6 micrometers, 7 micrometers, 8 micrometers, 9 micrometers, and 9.5 micrometers.

[0051] Optionally, the widths of the first region and the third region in the positive electrode width direction are both less than or equal to 0.05 times the width of the second region in the positive electrode width direction.

[0052] It should be understood that, in practice, the widths of the first and third regions in the width direction of the positive electrode sheet can be the same or different. When the widths of the first and third regions in the width direction of the positive electrode sheet are the same, the degree of lithium deposition on both sides of the negative electrode sheet can be more uniform, thereby improving the battery's lifespan.

[0053] The widths of the first and third regions in the positive electrode width direction can range from 0 mm to less than 5 mm. Specifically, the widths of the first and third regions in the positive electrode width direction can be any one of 1 mm, 2 mm, 2.5 mm, 3 mm, and 4 mm. Meanwhile, the width of the second region in the positive electrode width direction can range from 0 mm to less than 100 mm. Specifically, the width of the second region in the positive electrode width direction can be any one of 20 mm, 40 mm, 60 mm, 80 mm, and 100 mm.

[0054] By limiting the width of the first and third regions in the positive electrode width direction to be less than or equal to 0.05 times the width of the second region in the positive electrode width direction, the problem of lithium plating in the edge regions on both sides of the negative electrode can be alleviated while improving the energy density of the battery.

[0055] This application also provides a battery, including a negative electrode, an electrolyte, and a positive electrode as described in the first aspect, wherein the negative electrode and the positive electrode are disposed opposite to each other, and both the negative electrode and the positive electrode are placed in the electrolyte.

[0056] The battery provided in this application embodiment can be a wound battery or a stacked battery.

[0057] See Figure 3 The negative electrode includes a current collector 20 and two coatings respectively disposed on two surfaces of the current collector 20. The structure and working principle of the positive electrode provided in this application embodiment can be referred to the above embodiment, and will not be repeated here. Since the battery provided in this application embodiment includes the positive electrode provided in this application embodiment, the battery provided in this application embodiment has all the beneficial effects of the positive electrode provided in this application embodiment.

[0058] The battery provided in the embodiments of this application will be described below with reference to specific experiments.

[0059] Preparation of the negative electrode sheet: The slurry composition of the negative electrode active material layer is: 97wt% graphite, 1wt% conductive carbon black, and 2wt% styrene-butadiene latex. These components are added to a mixing tank at the specified mass ratio, followed by the addition of deionized water and stirring. The mixture is then passed through a 200-mesh sieve to prepare the negative electrode active material layer slurry, with a solid content of 40wt%-45wt%. The slurry is coated onto the negative electrode current collector (copper foil) using a transfer coating machine or an extrusion coating machine. After drying at 120℃, the negative electrode sheet is obtained by roller pressing. Its structure is as follows: Figure 3 As shown.

[0060] Preparation of the positive electrode sheet: Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride were added to a mixing tank at a mass ratio of 97.2:1.5:1.3. N-methylpyrrolidone solvent was added, and the mixture was stirred and passed through a 200-mesh sieve to prepare a slurry for the positive electrode active material layer, with a solid content of 70wt%-75wt%. The slurry was coated onto the positive electrode current collector (aluminum foil) using a coating machine, dried at 120℃, and then rolled to obtain the positive electrode sheet, the structure of which is as follows. Figure 1 and Figure 2 As shown.

[0061] In Examples 1-4, the widths of the first and third regions are equal.

[0062] Assemble the battery cell: The negative electrode sheet, positive electrode sheet and separator prepared above are wound together to form a core (width is 62mm), packaged with aluminum-plastic film, baked to remove moisture, injected with electrolyte, and hot-pressed to form the battery cell.

[0063] All lithium-ion battery positive and negative electrode sheets were fabricated into different cells, and the cell capacity was tested at 0.2C / 0.2C charge and discharge at 25℃. The energy density of the battery was calculated according to capacity * voltage / thickness / width / height. The cycle performance at 3C / 1C at 25℃ was also tested. The battery was disassembled after the same number of cycles to confirm the lithium deposition in the edge area of ​​the negative electrode sheet. The experimental results of the disassembly are shown in Table 1.

[0064]

[0065]

[0066] Table 1

[0067] As shown in Table 1, compared with Examples 1-4 and Comparative Example 1, coating the positive electrode active material with stronger delithiation capability in the edge region of the positive electrode (i.e., the first region and the third region) can significantly alleviate the problem of lithium deposition in the edge region on both sides of the negative electrode.

[0068] Comparing Examples 3 and 4, the degree of mitigation of lithium degradation problem increases as the width of the first and third regions increases.

[0069] Compared with Examples 1-4, increasing the width of the first and third regions increases the energy density of the battery. However, if the width of the first and third regions exceeds a certain limit (5 mm), i.e., becomes too wide, the lithium salt concentration difference of the electrolyte between the edge regions of the positive and negative electrodes and the middle regions of the positive and negative electrodes decreases, thus weakening the improvement effect on the lithium plating problem.

[0070] Therefore, when determining the widths of the first and third regions, it is necessary to consider selecting appropriate widths while meeting the performance requirement of preventing lithium plating. Example 3 provided in this application represents a preferred width value under the current design.

[0071] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A positive electrode plate, characterized in that, The device includes a current collector, the surface of which includes a first region, a second region, and a third region. The first region and the third region are located on opposite sides of the second region. The first region of the current collector is coated with a first coating, the second region of the current collector is coated with a second coating, and the third region of the current collector is coated with a third coating. The delithiation capabilities of the first coating and the third coating are both greater than those of the second coating. The first region, the second region, and the third region are all distributed along the width direction of the positive electrode sheet. The width of the first region and the third region in the width direction of the positive electrode sheet is less than or equal to 0.05 times the width of the second region in the width direction of the positive electrode sheet. The proportion of active material in the first coating and the proportion of active material in the third coating are both greater than the proportion of active material in the second coating.

2. The positive electrode sheet according to claim 1, characterized in that, The first coating has the same delithiation capability as the third coating.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The delithiation capacity of the active material in the first coating and the third coating is greater than that of the active material in the second coating.

4. The positive electrode sheet according to claim 3, characterized in that, The active material in the first coating and the third coating is a high-nickel ternary material, and the active material in the second coating includes at least one of medium-nickel ternary materials, low-nickel ternary materials, lithium cobalt oxide, and lithium iron phosphate. Alternatively, the active material in the first coating and the third coating is a medium-nickel ternary material, and the active material in the second coating includes at least one of low-nickel ternary materials, lithium cobalt oxide, and lithium iron phosphate; Alternatively, the active material in the first coating and the third coating may be lithium cobalt oxide, and the active material in the second coating may be lithium iron phosphate.

5. The positive electrode sheet according to claim 1, characterized in that, The mass percentage of active material in the first coating and the mass percentage of active material in the third coating both range from 98.5% to 97%. The mass percentage of the active material in the second coating ranges from 96% to 95%.

6. The positive electrode sheet according to claim 1, characterized in that, The thickness of both the first coating and the third coating is greater than the thickness of the second coating.

7. The positive electrode sheet according to claim 1, 5, or 6, characterized in that, The active materials in the first coating, the second coating, and the third coating all have the same delithiation capability.

8. A battery, characterized in that, It includes a negative electrode, an electrolyte, and a positive electrode as described in any one of claims 1 to 7, wherein the negative electrode and the positive electrode are disposed opposite to each other, and both the negative electrode and the positive electrode are placed in the electrolyte.

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