Negative plate and battery

Abstract

The utility model provides a negative plate. The negative plate comprises a negative current collector, a double-sided coating area negative active coating, a single-sided coating area negative active coating and a first coating, the thickness of the first coating is T0, the thickness of the negative active coating in the single-side coating area is T1, and T0 / T1 is equal to 1 / 3-4 / 5; and the elastic modulus of the first coating is less than or equal to that of the negative electrode active coating in the single-side coating area. According to the negative plate provided by the utility model, the first coating with relatively small elastic modulus is arranged on the surface of the current collector which is provided with the negative active coating in the back direction of the single-side coating area, and the thickness of the first coating is controlled, so that the compaction density of the first coating is approximately consistent with that of the negative active coating in the single-side coating area; the contact effect between particles and the current collector and between particles in the single-side coating region is improved, and the conduction of electrons in the single-side coating region is promoted, so that the battery keeps excellent energy density and cycle performance.

Description

Technical Field

[0001] The utility model belongs to the technical field of lithium ion batteries, and particularly relates to a negative electrode sheet and a battery. Background Art

[0002] In the current wound structure core, due to structural limitations, there are usually double-sided coating areas and single-sided coating areas. The double-sided coating area refers to the area where negative electrode active coatings are provided on both surfaces of the current collector that are oppositely arranged. The single-sided coating area refers to the area where the negative electrode active coating is provided on only one surface of the current collector. Since the single-sided coating area of the electrode sheet is thinner than the double-sided coating area, during the rolling process, if the rolling equipment cannot automatically adjust the roll gap, when ensuring the compaction of the double-sided coating area, the pressure on both sides of the current collector in the single-sided coating area during rolling is inconsistent, resulting in the inability to achieve the set compaction of the negative electrode active coating in the single-sided coating area. This phenomenon is particularly serious in negative electrode sheets with high surface density, resulting in poor electrical contact between particles and foil, and between particles in the single-sided coating area, and cyclic lithium deposition. Therefore, how to solve the above problems through the structural design of the negative electrode sheet has become an important research direction in this field. Summary of the Utility Model

[0003] The purpose of the utility model is to provide a negative electrode sheet, in which the negative electrode active coating in the single-sided coating area can reach the expected compaction density, so that the contact effect between particles and the current collector, and between particles in the single-sided coating area is good.

[0004] According to one aspect of the utility model, a negative electrode sheet is provided, which includes a negative electrode current collector, a double-sided coating area negative electrode active coating, a single-sided coating area negative electrode active coating, and a first coating; the negative electrode current collector includes a first surface and a second surface that are oppositely arranged. The double-sided coating area negative electrode active coating is provided on the first surface and the second surface. The single-sided coating area negative electrode active coating is provided on the first surface. The first coating is provided on the second surface. The single-sided coating area negative electrode active coating is arranged opposite to the first coating; along the length direction of the negative electrode sheet, the double-sided coating area negative electrode active coating and the single-sided coating area negative electrode active coating are arranged in sequence. Along the length direction of the negative electrode sheet, the double-sided coating area negative electrode active coating and the first coating are arranged in sequence; taking the thickness of the first coating as T0 and the thickness of the single-sided coating area negative electrode active coating as T1, T0 / T1 = 1 / 3 - 4 / 5; the elastic modulus of the first coating ≤ the elastic modulus of the single-sided coating area negative electrode active coating.

[0005] The present utility model provides a negative electrode sheet with a specific structure. By disposing a first coating with a relatively small elastic modulus on the surface of a current collector having a single-sided coated negative electrode active coating on the back side and controlling the thickness of the first coating, it is beneficial to make the compaction density of the first coating and the single-sided coated negative electrode active coating close to the same, improve the contact effect between the particles and the current collector and between the particles in the single-sided coated area, promote the conduction of electrons in the single-sided coated area, avoid problems such as lithium plating on the negative electrode from deteriorating the battery cycle performance, and thus enable the battery to maintain excellent energy density and cycle performance.

[0006] If the first coating is too thick, the thickness of the battery cell will be lost, resulting in a large loss of battery energy density; if the first coating is too thin, the thickness difference between the first coating and the single-sided coated negative electrode active coating is relatively large, and it is difficult to ensure the same compaction of the first coating and the single-sided coated negative electrode active coating.

[0007] Preferably, the elastic modulus of the single-sided coated negative electrode active coating is 6 - 15 GPa. The single-sided coated negative electrode active coating with the above elastic modulus has good mechanical properties, which is beneficial to preventing problems such as deformation or displacement due to a large degree of compression during the rolling process.

[0008] Preferably, the elastic modulus of the first coating is 3 - 6 GPa. The first coating with the above elastic modulus has good mechanical properties, which is beneficial to preventing problems such as deformation or displacement due to a large degree of compression during the rolling process.

[0009] Preferably, T0 / T1 = 2 / 5 - 3 / 5. By controlling the thickness ratio of the first coating and the single-sided coated negative electrode active coating, it is beneficial to make the compaction density of the single-sided coated negative electrode active coating and the double-sided coated negative electrode active coating close to the same, promote good contact between the particles and the current collector and between the particles in the single-sided coated area, and further optimize the cycle performance of the battery.

[0010] Preferably, the thickness of the single-sided coated negative electrode active coating is 40 - 70 μm. If the single-sided coated negative electrode active coating is too thick, it is not conducive to the transmission of electrons and the conduction of ions, increasing the impedance level of the electrode sheet and reducing the cycle performance; if the single-sided coated negative electrode active coating is too thin, it is not conducive to the exertion of the electrode sheet capacity.

[0011] Preferably, the thickness of the first coating is 20 - 35 μm.

[0012] Preferably, the first coating is a ceramic layer, a boehmite layer or an inorganic oxide layer.

[0013] Preferably, the length of the first coating is equal to the length of the single-sided coated negative electrode active coating. The first coating with this length is beneficial to fully protecting the single-sided coated negative electrode active coating during the rolling process and alleviating problems such as deformation or pulverization caused by a large degree of compression.

[0014] Preferably, the negative electrode sheet further includes a tab.

[0015] Preferably, the ratio of the compaction density of the first coating layer to the negative electrode active coating layer in the single-sided coating area is ≥ 92%.

[0016] According to another aspect of the present utility model, a battery is provided, which includes the above-mentioned negative electrode sheet. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of the negative electrode sheets prepared in Examples 1-9 and Comparative Examples 2-4.

[0018] Figure 2 It is a schematic structural diagram of the negative electrode sheet prepared in Comparative Example 1.

[0019] In the above-mentioned drawings, the corresponding relationship between the technical features and the reference numerals is as follows: 1 is the negative electrode active coating layer in the single-sided coating area, 2 is the negative electrode active coating layer in the double-sided coating area, 3 is the first coating layer, 4 is the current collector, and 5 is the tab. Detailed Embodiments

[0020] The technical features in the technical solutions provided by the present utility model are further clearly and completely described below in conjunction with the detailed embodiments. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present utility model.

[0021] Example 1

[0022] This example provides a lithium-ion battery, and its preparation method includes the following steps:

[0023] (1) Preparation of the negative electrode sheet

[0024] In the negative electrode paste used in this example for preparing the negative electrode sheet, the negative electrode active material is graphite, the binder is SBR, and the conductive agent is SP. Calculated by mass ratio, the negative electrode active material: binder: conductive agent = 97%: 2.0%: 1%.

[0025] S1. Use an 8-μm copper foil as the negative electrode current collector 4, and then coat the above-mentioned negative electrode paste on two opposite surfaces of the negative electrode current collector 4 respectively, and dry it. Thus, negative electrode active coating layers with unequal coating areas are formed on both sides of the negative electrode current collector 4 respectively. Therefore, in the negative electrode sheet, part of the area is a double-sided coating area where negative electrode active coating layers are provided on both sides of the current collector, and part of the area is a single-sided coating area where a negative electrode active coating layer is provided only on one side of the current collector. In this example, the thickness of the negative electrode active coating layers provided on both sides of the current collector is 50 μm.

[0026] S2. A first coating is provided on the surface of the current collector with a single-sided coated negative electrode active coating on the back side; taking the thickness of the first coating as T0 and the thickness of the single-sided coated negative electrode active coating as T1, T0 = 30 μm and T1 = 50 μm; the elastic modulus of the first coating is 5 GPa, and the elastic modulus of the single-sided coated negative electrode active coating is 8 GPa, thus obtaining a negative electrode sheet.

[0027] (2) Preparation of the positive electrode sheet

[0028] In the positive electrode active paste used to prepare the positive electrode sheet in this embodiment, the positive electrode active material is lithium cobaltate, the binder is PVDF, and the conductive agent is SP. Calculated by mass ratio, positive electrode active material: binder: conductive agent = 97%: 1%: 2%.

[0029] (3) Assembly and formation of the battery

[0030] The battery of this product is made by a common winding structure manufacturing process: batching - coating - rolling - slitting - sheet making - core winding - assembly - liquid injection - formation - shaping.

[0031] The negative electrode sheet obtained in this embodiment has a structure as Figure 1 shown. The negative electrode sheet includes a negative electrode current collector 4, a double-sided coated negative electrode active coating 2, a single-sided coated negative electrode active coating 1, a first coating 3, and a tab 5; the negative electrode current collector 4 includes a first surface and a second surface arranged opposite to each other, the double-sided coated negative electrode active coating 2 is provided on the first surface and the second surface, the single-sided coated negative electrode active coating 1 is provided on the first surface, the first coating 3 is provided on the second surface, the first coating 3 is arranged opposite to the single-sided coated negative electrode active coating 1, along the length direction of the negative electrode sheet, the double-sided coated negative electrode active coating 2 and the single-sided coated negative electrode active coating 1 are arranged in sequence, and along the length direction of the negative electrode sheet, the double-sided coated negative electrode active coating 2 and the first coating 3 are arranged in sequence.

[0032] Example 2

[0033] This example prepares a lithium-ion battery with reference to Example 1. The difference between this example and Example 1 is that the thickness of the first coating in this example is 17 μm. Except for the above difference, the materials and process operations used in this example are strictly the same as those in Example 1.

[0034] Example 3

[0035] This example prepares a lithium-ion battery with reference to Example 1. The difference between this example and Example 1 is that the thickness of the first coating in this example is 23 μm. Except for the above difference, the materials and process operations used in this example are strictly the same as those in Example 1.

[0036] Example 4

[0037] In this example, a lithium-ion battery was prepared with reference to Example 1. The difference between this example and Example 1 is that the thickness of the first coating in this example is 28 μm. Except for the above difference, the materials and process operations used in this example are strictly the same as those in Example 1.

[0038] Example 5

[0039] In this example, a lithium-ion battery was prepared with reference to Example 1. The difference between this example and Example 1 is that the thickness of the first coating in this example is 40 μm. Except for the above difference, the materials and process operations used in this example are strictly the same as those in Example 1.

[0040] Example 6

[0041] In this example, a lithium-ion battery was prepared with reference to Example 1. The difference between this example and Example 1 is that the elastic modulus of the first coating in this example is 2 GPa. Except for the above difference, the materials and process operations used in this example are strictly the same as those in Example 1.

[0042] Example 7

[0043] In this example, a lithium-ion battery was prepared with reference to Example 1. The difference between this example and Example 1 is that the elastic modulus of the first coating in this example is 3 GPa. Except for the above difference, the materials and process operations used in this example are strictly the same as those in Example 1.

[0044] Example 8

[0045] In this example, a lithium-ion battery was prepared with reference to Example 1. The difference between this example and Example 1 is that the elastic modulus of the first coating in this example is 6 GPa. Except for the above difference, the materials and process operations used in this example are strictly the same as those in Example 1.

[0046] Example 9

[0047] In this example, a lithium-ion battery was prepared with reference to Example 1. The difference between this example and Example 1 is that the elastic modulus of the first coating in this example is 7 GPa. Except for the above difference, the materials and process operations used in this example are strictly the same as those in Example 1.

[0048] Comparative Example 1

[0049] In this comparative example, a lithium-ion battery was prepared with reference to Example 1. The difference between this comparative example and Example 1 is that the negative electrode sheet in this comparative example is not provided with a first coating. Except for the above difference, the materials and process operations used in this comparative example are strictly the same as those in Example 1.

[0050] The negative electrode sheet with the structure obtained in this comparative example is as follows Figure 2 shown. The negative electrode sheet includes a negative electrode current collector 4, a negative electrode active coating 2 in a double-sided coating area, a negative electrode active coating 1 in a single-sided coating area, and a tab 5; the negative electrode current collector 4 includes a first surface and a second surface arranged opposite to each other, the negative electrode active coating 2 in the double-sided coating area is arranged on the first surface and the second surface, the negative electrode active coating 1 in the single-sided coating area is arranged on the first surface, and along the length direction of the negative electrode sheet, the negative electrode active coating 2 in the double-sided coating area and the negative electrode active coating 1 in the single-sided coating area are arranged in sequence.

[0051] Comparative Example 2

[0052] This comparative example prepares a lithium-ion battery with reference to Example 1. The difference between this comparative example and Example 1 is that: the thickness of the first coating in this comparative example is 14 μm. Except for the above differences, the materials and process operations used in this comparative example are strictly the same as those in Example 1.

[0053] Comparative Example 3

[0054] This comparative example prepares a lithium-ion battery with reference to Example 1. The difference between this comparative example and Example 1 is that: the thickness of the first coating in this comparative example is 48 μm. Except for the above differences, the materials and process operations used in this comparative example are strictly the same as those in Example 1.

[0055] Comparative Example 4

[0056] This comparative example prepares a lithium-ion battery with reference to Example 1. The difference between this comparative example and Example 1 is that: the elastic modulus of the first coating in this comparative example is 18 GPa. Except for the above differences, the materials and process operations used in this comparative example are strictly the same as those in Example 1.

[0057] Test Example

[0058] 1. Test object:

[0059] The lithium-ion batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 4 are used as the test objects of this test example.

[0060] 2. Test items

[0061] (1) Energy density: Energy density = Capacity * Plateau voltage / (Cell length * Cell thickness * Cell width).

[0062] (2) Cycle performance: At 25 °C, charge at 1C to 4.45V, discharge at 1C to 3V, cycle 500 times, and record the capacity retention rate of the battery after 500 cycles.

[0063] 3. Test results

[0064] Table 1 Performance test results of Examples 1-9 and Comparative Examples 1-4

[0065]

[0066]

[0067] The test results are shown in Table 1. By comparing the performance test results corresponding to Example 1 and Comparative Example 1, it can be found that the cycle capacity retention rate of the battery prepared in Comparative Example 1 is lower than that in Example 1. The reason is that the first coating is not provided on the negative electrode sheet prepared in Comparative Example 1, resulting in inconsistent pressure on both sides of the current collector belonging to the single-sided coating area during rolling, and poor contact effects between the particles and the foil, and between the particles in the single-sided coating area, making the cycle characteristics of the battery prepared therefrom deteriorate.

[0068] By comparing the performance test results corresponding to Example 1 and Comparative Examples 2-3, it can be found that the cycle capacity retention rate of the batteries prepared in Comparative Examples 2-3 is lower than that in Example 1. The reason is that the ratios of the thickness T0 of the first coating to the thickness T1 of the negative electrode active coating in the single-sided coating area in Comparative Examples 2 and 3 do not satisfy T0 / T1 = 1 / 3 - 4 / 5, resulting in inconsistent pressure on the first coating and the negative electrode active coating in the single-sided coating area during rolling, causing lithium deposition in the single-sided coating area during cycling, and making the cycle characteristics of the battery prepared therefrom deteriorate.

[0069] By comparing the performance test results corresponding to Example 1 and Comparative Example 4, it can be found that the cycle capacity retention rate of the battery prepared in Comparative Example 4 is lower than that in Example 1. The reason is that the elastic modulus of the first coating in Comparative Example 4 is too large, which is not conducive to effectively controlling the compaction density of the negative electrode active coating in the single-sided coating area and the first coating, thus deteriorating the cycle characteristics of the battery prepared therefrom.

[0070] By comparing the performance test results of Example 1 and Examples 2-5. As can be seen from Table 1, under the condition that other materials and operations for preparing the battery are the same, T0 / T1 < 2 / 5 in Example 2, and the cycle capacity retention rate of the lithium-ion battery prepared therefrom is slightly lower than that in Examples 1, 3-4; T0 / T1 > 4 / 5 in Example 5, and the energy density and cycle capacity retention rate of the lithium-ion battery prepared therefrom are slightly lower than that in Examples 1, 3-4. This shows that, compared with Examples 2 and 5, Examples 1, 3-4 can, by controlling the thickness ratio of the first coating to the negative electrode active coating in the single-sided coating area, fully protect the negative electrode active coating in the single-sided coating area during rolling on the premise of ensuring the energy density of the battery, and prevent problems such as the deterioration of the cycle stability of the battery caused by its displacement and deformation.

[0071] Compare the performance test results of Example 1 with those of Examples 6 to 9. As can be seen from Table 1, under the condition that other materials and operations for preparing the battery are the same, the elastic modulus of the first coating in Example 6 is < 2 GPa, and the elastic modulus of the first coating in Example 9 is > 6 GPa. The energy density and cycle capacity retention rate of the batteries thus prepared are slightly lower than those of Examples 1, 7 to 8. This shows that, compared with Examples 5 to 6, Examples 1, 7 to 8 by using the first coating with a suitable elastic modulus are beneficial to ensuring the mechanical properties of the first coating, enabling it to play a sufficient protective role for the negative electrode active coating in the single-sided coating area, and improving the cycle stability of the batteries prepared.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced, but these modifications or replacements are all within the protection scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that the negative electrode sheet includes a negative electrode current collector, a negative electrode active coating in a double-sided coating area, a negative electrode active coating in a single-sided coating area, and a first coating; the negative electrode current collector includes a first surface and a second surface arranged oppositely, the negative electrode active coating in the double-sided coating area is provided on the first surface and the second surface, the negative electrode active coating in the single-sided coating area is provided on the first surface, the first coating is provided on the second surface, and the negative electrode active coating in the single-sided coating area is arranged oppositely to the first coating; along the length direction of the negative electrode sheet, the negative electrode active coating in the double-sided coating area and the negative electrode active coating in the single-sided coating area are arranged in sequence, along the length direction of the negative electrode sheet, the negative electrode active coating in the double-sided coating area and the first coating are arranged in sequence; taking the thickness of the first coating as T0 and the thickness of the negative electrode active coating in the single-sided coating area as T1, T0 / T1 = 1 / 3 - 4 / 5; the elastic modulus of the first coating ≤ the elastic modulus of the negative electrode active coating in the single-sided coating area.

2. The negative electrode sheet according to claim 1, characterized in that, The elastic modulus of the negative electrode active coating in the single-sided coating area is 6 - 15 Gpa.

3. The negative electrode sheet according to claim 2, wherein, The elastic modulus of the first coating is 3 - 6 Gpa.

4. The negative electrode sheet according to claim 1, characterized in that, T0 / T1 = 2 / 5 - 3 / 5.

5. The negative electrode sheet according to claim 4, wherein, The thickness of the negative electrode active coating in the single-sided coating area is 40 - 70 μm.

6. The negative electrode sheet according to claim 5, wherein, The thickness of the first coating is 20 - 35 μm.

7. The negative electrode sheet according to claim 1, wherein The first coating is a ceramic layer, a boehmite layer or an inorganic oxide layer.

8. The negative electrode sheet according to claim 1, wherein, The negative electrode sheet further includes a tab.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that, The ratio of the compaction density of the first coating to that of the negative electrode active coating in the single-sided coating area ≥ 92%.

10. A battery, characterized in that, Including the negative electrode sheet according to any one of claims 1 - 9.

Images