Electrode tab, lithium battery and power vehicle

Abstract

The application provides an electrode tab, a lithium battery and a power vehicle. The electrode tab comprises a current collector and an electrode active material layer arranged on at least one side surface of the current collector. The electrode active material layer comprises at least two electrode active material sub-layers. The electrode active material sub-layers satisfy: n×δ i ≤10000, n≥2, δ i ≤5000; and H i‑1 +δ i ‑k≤H i ≤H i‑1 +δ i +k, 0<50≤k, H i‑1 <H i ; the first electrode active material sub-layer is in contact with the current collector. The electrode tab has a high maximum compaction density and a high electrode active material particle integrity. The electrode tab can be used to provide a battery with high energy density and long cycle life.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, specifically to an electrode sheet, a lithium battery, and a power vehicle. Background Technology

[0002] With the development of the new energy industry, the market demand for the energy density of lithium batteries is increasing. Improving the compaction density of electrode sheets is one of the important ways to increase the energy density of lithium batteries. However, during the preparation of electrode sheets, when the electrode sheets are rolled, the stress on the electrode active material loaded on them is uneven along the thickness direction of the electrode sheet. This can easily lead to the breakage of the surface electrode active material particles, thus affecting the stability of the electrode active material. Furthermore, the broken electrode active material will consume more electrolyte and may even affect the porosity of the electrode sheet, increasing the battery's internal resistance, hindering battery capacity utilization, and shortening battery life. Summary of the Invention

[0003] In view of this, this application provides an electrode sheet, a lithium battery, and a power vehicle. The electrode sheet has multiple electrode active material sub-layers, and the hardness of each electrode active material sub-layer increases from the side near the current collector along the thickness direction of the electrode sheet, so that the electrode sheet has a high maximum compaction density. The electrode active material loaded thereon also has high particle integrity. The electrode sheet can be used to provide batteries with high energy density and long cycle life.

[0004] Specifically, the first aspect of this application provides an electrode sheet, the electrode sheet comprising a current collector and an electrode active material layer disposed on at least one surface of the current collector; the electrode active material layer comprises at least two electrode active material sublayers, the electrode active material sublayers satisfying the following relationship:

[0005] n×δ i ≤10000, n≥2, δ i ≤5000;

[0006] And H i-1 +δ i -k≤H i ≤H i-1 +δ i +k, 0 < 50 ≤ k, H i-1 <H i ;

[0007] Where n represents the total number of sublayers of the electrode active material, i is any integer value between 2 and n, and H iH1 represents the hardness of the i-th electrode active material sublayer, and H1 represents the hardness of the 1-th electrode active material sublayer, both in MPa; k is an error factor in MPa; wherein, the 1-th electrode active material sublayer is in contact with the current collector; δ i This represents the absolute value of the hardness difference between the i-th electrode active material sublayer and the (i-1)-th electrode active material sublayer, in MPa.

[0008] The hardness of the multiple electrode active material sublayers in this electrode sheet gradually increases from the current collector towards the electrode active material layer, resulting in a high maximum compaction density and high integrity of the electrode active material loaded on it. This electrode sheet can improve the energy density of the battery and extend its cycle life.

[0009] Optionally, the δ i ≤50.

[0010] Optionally, the value of α satisfies: 0 g / cm³ 3 <α<10g / cm 3 Preferably, the value of α satisfies: 0 g / cm³ 3 <α<5g / cm 3 .

[0011] Optionally, the n, the δ i The following quantitative relationship is satisfied between the maximum compaction density α of the electrode sheet and the density of the electrode sheet: when 1.3 g / cm³ 3 ≤α<1.8g / cm 3 Or 2.6g / cm 3 ≤α<2.8g / cm 3 Or 3.65g / cm 3 ≤α<5g / cm 3 When n≥10, δ i ≤5.

[0012] Optionally, the n, the δ i The following quantitative relationship exists between the maximum compaction density α of the electrode sheet and the density of the electrode sheet: when 5 g / cm³ 3 ≤α<10g / cm 3 When n≥15, δ i ≤2.

[0013] Optionally, in the electrode sheet, the absolute value of the hardness difference between any two adjacent electrode active material sublayers is equal.

[0014] Optionally, the electrode active material includes a positive electrode active material or a negative electrode active material; wherein, the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxygen ternary material, lithium nickel cobalt aluminum oxygen ternary material, and lithium nickel manganese cobalt aluminum oxygen quaternary material; the negative electrode active material includes at least one of graphite, natural graphite, mesophase carbon microspheres, and silicon-carbon negative electrode material.

[0015] Optionally, the positive electrode active material includes a magnesium-doped multi-component nickel-containing active material, wherein the multi-component nickel-containing active material includes at least one of lithium nickel manganese cobalt oxygen ternary material, lithium nickel cobalt aluminum oxygen ternary material, and lithium nickel manganese cobalt aluminum oxygen quaternary material.

[0016] Optionally, the magnesium element in the magnesium-doped multi-component nickel-containing active material has a mass content greater than 0 and less than 4000 ppm.

[0017] A second aspect of this application provides a lithium battery having the electrode plates provided in the first aspect of this application. This battery exhibits high energy density and a long cycle life.

[0018] A third aspect of this application provides a powered vehicle having the lithium battery provided in the second aspect of this application. This powered vehicle has a long driving range. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of the electrode sheet provided in the embodiment of this application.

[0020] The reference numerals in the attached figures are explained as follows: 100 - electrode electrode sheet; 10 - electrode active material layer; 11 - current collector; 101 - first electrode active material sublayer; 102 - second electrode active material sublayer; 10n - nth electrode active material sublayer. Detailed Implementation

[0021] The technical solution of this application will be described in detail below with reference to specific embodiments.

[0022] Generally, each electrode active material has a specific range of compaction density that it can achieve. When a single electrode active material cannot achieve the maximum compaction density of the electrode sheet while ensuring the integrity of the electrode active material particles, constructing an electrode sheet with gradient hardness can effectively solve the above problem.

[0023] This application provides an electrode sheet, the electrode sheet comprising a current collector and an electrode active material layer disposed on at least one surface of the current collector; the electrode active material layer comprises at least two electrode active material sublayers, the electrode active material sublayers satisfying the following relationship:

[0024] n×δ i ≤10000, n≥2, δ i ≤5000;

[0025] And H i-1 +δ i -k≤H i ≤H i-1 +δ i +k, 0 < 50 ≤ k, H i-1 <H i (Relation 1)

[0026] Where n represents the total number of sublayers of the electrode active material, i is any integer value between 2 and n, and H i H1 represents the hardness of the i-th electrode active material sublayer, and H1 represents the hardness of the 1-th electrode active material sublayer, both in MPa; k is an error factor in MPa; wherein, the 1-th electrode active material sublayer is in contact with the current collector; δ i This represents the absolute value of the hardness difference between the i-th electrode active material sublayer and the (i-1)-th electrode active material sublayer, in MPa.

[0027] The electrode sheet has multiple sub-layers of electrode active material. The sub-layer of electrode active material in contact with the current collector is defined as the first electrode active material sub-layer. Along the thickness direction of the electrode sheet, the sub-layers from the current collector side to the electrode sheet surface are respectively the 2nd, 3rd, 4th, 5th, ..., nth electrode active material sub-layers, and the hardness of the first to the nth electrode active material sub-layers gradually increases (e.g., ...). Figure 1As shown, the electrode sheet 100 includes a current collector 11 and an electrode active material layer 10 disposed on the current collector 11. The electrode active material layer 10 is composed of a first electrode active material sublayer 101 to an nth electrode active material sublayer 10n. When the absolute value of the hardness difference between each electrode active material sublayer satisfies the above-mentioned relationship 1, it can be ensured that the hardness difference between two adjacent electrode active material sublayers is within an acceptable range. During the rolling process of the electrode sheet, the surface electrode active material sublayer experiences the greatest pressure. As this pressure is transmitted to the current collector side, the pressure on each electrode active material sublayer decreases layer by layer. The pressure on each sublayer matches the hardness of that sublayer, and the electrode active material in each sublayer is not easily broken. While the overall electrode sheet has a high maximum compaction density, the particle integrity of the electrode active material can be ensured, thereby improving the energy density of the battery and extending the cycle life of the battery. When the hardness difference between the sub-layers of each electrode active material is too large (not satisfying the above relationship 1), then during the rolling process of the electrode sheet, the i-th sub-layer can withstand a large pressure, but when this pressure is transmitted to the (i-1)-th electrode active material sub-layer, the pressure it withstands is greater than the hardness of the (i-1)-th electrode active material sub-layer, and the rupture of the electrode active material in that sub-layer cannot be avoided, thus affecting the performance of the lithium battery.

[0028] In this application, electrode active material generally refers to electrode active material particles, and the aforementioned rupture of electrode active material generally refers to the rupture of electrode active material particles. The hardness of each electrode active material sublayer can be regarded as the hardness of the electrode active material particles themselves. Specifically, the test method for the hardness of the electrode active material sublayer (i.e., the hardness of the electrode active material particles themselves) is as follows:

[0029] 1) Starting from the outermost edge of the outermost electrode sheet, collect the electrode active material particles of each electrode active material sublayer;

[0030] 2) Hardness testing of individual electrode active material particles was performed using in-situ field emission scanning electron microscopy (FESEM). The specific testing steps are as follows: A pointer equipped with a pressure sensor was used to apply linearly increasing pressure to a single electrode active material particle until the electrode active material fractured. At this point, the pressure at the pointer tip changed abruptly, and the stress curve of the electrode active material fed back by the pressure sensor showed an inflection point. At this point, the pressure applied to the electrode active material particle was stopped, and the fracture state of the electrode active material was observed.

[0031] 3) Record the pressure value at the inflection point of the force curve as the crushing pressure of the electrode active material particles. Calculate the hardness value H0 of the electrode active material particles using the following formula: H0 = 2.8P(πr 2), where P is the particle crushing pressure in N; r is the particle diameter in μm; and H0 is in MPa.

[0032] 4) Take at least 500 electrode active material particle samples from each electrode active material sublayer, test their hardness according to the steps above, and take the arithmetic mean. This arithmetic mean represents the hardness of the corresponding electrode active material sublayer. In particular, when the electrode active material sublayer is a mixture of different electrode active material particles, the hardness of the sublayer is the mass-weighted average hardness value of each electrode active material particle.

[0033] In this application, δ i δ represents the absolute value of the hardness difference between the i-th electrode active material sublayer and the (i-1)-th electrode active material sublayer, specifically, δ1 = |H2 - H1|, δ2 = |H3 - H2|, ..., δ n =|H n -H n-1 And so on. The above δ i The values ​​can be the same or different.

[0034] In this application, each electrode active material sublayer can be composed of a single electrode active material or a mixture of different electrode active materials. The materials used for electrode activity within each electrode active material sublayer can be different or the same. For certain specific electrode active materials, the hardness of the electrode active material itself can be changed by altering its preparation process, or by doping or coating it, thereby enabling the construction of electrode sheets containing a single type of electrode active material and exhibiting a gradient hardness.

[0035] In some embodiments of this application, the δ i ≤50. At this point, the hardness difference between two adjacent electrode active material sublayers is smaller, which is more conducive to ensuring the integrity of the electrode active material particles.

[0036] In this embodiment of the application, the maximum compaction density α of the electrode sheet satisfies: 0 g / cm³ 3 <α<10g / cm 3 In some specific embodiments of this application, the value of α satisfies: 0 g / cm³ 3 <α<5g / cm 3 .

[0037] In some embodiments of this application, n and δ i The following quantitative relationship is satisfied between α and α: when 1.3 g / cm 3 ≤α<1.8g / cm 3 Or 2.6g / cm 3 ≤α<2.8g / cm3 Or 3.65g / cm 3 ≤α<5g / cm 3 When n≥10, δ i ≤5. In other embodiments of this application, when 5g / cm 3 ≤α<10g / cm 3 When n≥15, δ i ≤2.

[0038] Under the same conditions, the more sublayers (n) of the electrode active material, the smaller the absolute value of the hardness difference between adjacent layers, and the smaller the hardness gradient of the electrode active material layers in the thickness direction. Understandably, the maximum compaction density α of the electrode sheet is related to the specific type of electrode active material used. When certain electrode active materials are selected, the maximum compaction density of the electrode sheet that can be produced will fall within a certain range mentioned above, and n and δ are determined according to their material properties. i The value of is chosen so that it falls within the aforementioned range, which is more conducive to the preparation of the aforementioned electrode sheet.

[0039] In some embodiments of this application, the absolute value of the hardness difference between any two adjacent sublayers of the electrode active material in the electrode sheet is equal. Specifically, |H2-H1|=|H3-H2|=…=|H n -H n-1 At this point, the uniformity of the hardness gradient of the electrode sheet can be further improved, and the design of the electrode sheet can also be simplified.

[0040] In some embodiments of this application, the electrode active material includes a positive electrode active material or a negative electrode active material. It is understood that when the electrode sheet is a positive electrode sheet, the electrode active material is a positive electrode active material; when the electrode sheet is a negative electrode sheet, the electrode active material is a negative electrode active material. The positive electrode active material and the negative electrode active material are commonly used materials in the battery field.

[0041] The positive electrode active material includes, but is not limited to, at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxygen ternary materials, lithium nickel cobalt aluminum oxygen ternary materials, and lithium nickel manganese cobalt aluminum oxygen quaternary materials; the negative electrode active material includes, but is not limited to, at least one of graphite, natural graphite, mesophase carbon microspheres, and silicon-carbon negative electrode materials. The aforementioned positive or negative electrode active materials can be undoped or uncoated electrode active materials, or they can be doped or coated electrode active materials.

[0042] In some embodiments of this application, the positive electrode active material includes, but is not limited to, magnesium-doped multi-component nickel-containing active materials. These multi-component nickel-containing active materials include, but are not limited to, at least one of lithium nickel manganese cobalt-oxygen ternary materials, lithium nickel cobalt-aluminum-oxygen ternary materials, and lithium nickel manganese cobalt-aluminum-oxygen quaternary materials. In this application, the aforementioned multi-component nickel-containing active materials refer to ternary or higher (generally ternary or quaternary) nickel-containing active materials. NCM represents lithium nickel cobalt-manganese-oxygen ternary materials; in some embodiments, its general structural formula can be represented as Li… 1+m Ni x Co y Mn 1-x-y O2 (x≥0.33, 0≤y≤0.4, 0≤m≤0.1). NCA represents lithium-nickel-cobalt-aluminum-oxygen ternary materials; in some embodiments, its general structural formula can be represented as Li 1+m Ni x Co y Al 1-x-y O2 (x≥0.33, 0≤y≤0.4, 0≤m≤0.1). NCMA represents a lithium-nickel-manganese-cobalt-aluminum-oxygen quaternary material; in some embodiments, its general structural formula can be represented as Li 1+m Ni x Co y Mn z Al 1-x-y-z O2(x≥0.33, 0≤y≤0.4, 0≤z≤0.4, 0≤m≤0.1).

[0043] Preferably, the value of x is in the range of 0.70 ≤ x ≤ 0.98. Furthermore, when the value of x is high, the aforementioned multi-element nickel-containing material can also be called a "multi-element high-nickel material".

[0044] In some embodiments of this application, when the electrode active material used is the above-mentioned Mg-doped multi-component nickel-containing active material, the mass content of magnesium element in the magnesium-doped multi-component nickel-containing active material is greater than 0 and less than 4000 ppm.

[0045] Generally, the higher the Mg doping amount, the greater the hardness of the Mg-doped multi-element nickel-containing active material particles. In the electrode sheet described in this application, the Mg doping amount in each electrode active material sublayer increases sequentially from the 1st to the nth electrode active material sublayer. Thus, the hardness of each electrode active material sublayer increases sequentially from the 1st to the nth electrode active material sublayer. Therefore, by adjusting the Mg doping amount in the multi-element nickel-containing active material, the hardness of the multi-element nickel-containing active material can be precisely controlled, thereby enabling the precise construction of electrode sheets containing only a single type of active material and exhibiting gradient hardness. Similarly, by using other metal elements for doping, or by using other methods such as coating or modifying the electrode active material preparation, the aforementioned electrode sheets containing only a single electrode active material can also be prepared.

[0046] In preparing the aforementioned electrode sheet, an electrode active material layer can be formed on the surface of the current collector using a coating method. This coating includes drop coating, brush coating, spray coating, dip coating, blade coating, and spin coating. The specific coating method depends on the raw materials of the electrode active material sublayer, which contain electrode active materials, binders, and optionally conductive agents. These raw materials can be liquid or solid.

[0047] In some embodiments of this application, the aforementioned raw material is a liquid raw material containing a solvent, which can be formed on the current collector by methods such as drop coating, brush coating, spray coating, dip coating, scraping coating, spin coating, etc. Specifically, each electrode active material sublayer can be coated layer by layer on the surface of the current collector, and dried layer by layer to form an electrode active material layer; alternatively, a multilayer coating die can be used to coat multiple layers of electrode active material sublayers at once and then dry them to form an electrode active material layer. In other embodiments, when the aforementioned raw material is a solid raw material, the solid raw material can be formed on the current collector by methods such as powder spraying (i.e., the electrode active material layer is prepared using a dry method).

[0048] This application also provides a lithium battery having the electrode plates provided in this application. In some embodiments, the positive electrode plate of the lithium battery is the electrode plate provided in this application, and the negative electrode plate is a conventional electrode plate. In some embodiments, the negative electrode plate of the lithium battery is the electrode plate provided in this application, and the positive electrode plate is a conventional electrode plate. In some embodiments, both the positive and negative electrode plates of the lithium battery are electrode plates provided in this application.

[0049] The aforementioned batteries have superior energy density and long cycle life.

[0050] This application also provides a power vehicle equipped with the lithium battery provided in this application embodiment. The lithium battery includes the electrode plates provided in this application embodiment. This power vehicle has a long driving range.

[0051] The embodiments provided in this application will be described in detail below.

[0052] First, a series of ternary nickel-containing materials (LiNi) with different Mg doping amounts were prepared. 0.8 Co 0.1 Mn 0.1O2 (NCM811) was used to measure the hardness of the doped NCM811. When the Mg doping amount was 400 ppm, the hardness of NCM811 was approximately 100 MPa; when the Mg doping amount was approximately 700 ppm, the hardness of NCM811 was 125 MPa; when the Mg doping amount was 1000 ppm, the hardness of NCM811 was approximately 150 MPa; when the Mg doping amount was 1500 ppm, the hardness of NCM811 was approximately 175 MPa, and so on.

[0053] Example 1

[0054] (1) Preparation of the positive electrode sheet: 100g of NCM811, 1g of conductive agent Super P, and 0.5g of binder PVDF5130 were added to N-methylpyrrolidone (NMP) and mixed evenly to obtain the positive electrode slurry. The preset maximum compaction density of the electrode sheet was 3.6g / cm³. 3 The above-mentioned positive electrode slurry was applied to the surface of the positive electrode current collector (aluminum foil) using a three-layer coating die. After drying, rolling, and slitting, a positive electrode sheet with three sub-layers of active electrode material was obtained. The average particle hardness of the first sub-layer of active electrode material in this positive electrode sheet is 175 MPa, the average particle hardness of the second sub-layer is 200 MPa, and the average particle hardness of the third sub-layer is 225 MPa.

[0055] (2) Preparation of the negative electrode sheet: 100g of graphite negative electrode active material, 1g of thickener, and 1g of emulsion are added to water in a certain order and mixed evenly to obtain a negative electrode active slurry. The above negative electrode active material is uniformly coated on the surface of the negative electrode current collector - copper foil. After drying, it is pressed into a sheet by a roller press to obtain the negative electrode sheet.

[0056] (3) Battery fabrication: The positive electrode obtained in step (1) and the negative electrode obtained in step (2) are alternately stacked with a separator to prepare the battery. The positive and negative electrodes are arranged alternately, and adjacent positive and negative electrodes are separated by a separator to obtain a dry cell. The dry cell is placed in an aluminum-plastic film outer packaging, electrolyte is injected, and then it is vacuum sealed. After being placed at 60°C for 48 hours, it is pressurized at 60°C, repackaged, vented, and capacity tested to obtain a stacked soft-pack full battery with a capacity of 2.2Ah. The prepared battery is denoted as S1.

[0057] Example 2

[0058] The difference from Example 1 is that the average particle hardness of the first electrode active material sublayer in this positive electrode sheet is 175 MPa, the average particle hardness of the second electrode active material sublayer is 200 MPa, and the average particle hardness of the third electrode active material sublayer is 250 MPa. The resulting battery is denoted as S2.

[0059] Example 3

[0060] The difference from Example 1 is that the average particle hardness of the first electrode active material sublayer in this positive electrode sheet is 175 MPa, the average particle hardness of the second electrode active material sublayer is 225 MPa, and the average particle hardness of the third electrode active material sublayer is 250 MPa. The resulting battery is designated as S3.

[0061] Example 4

[0062] The difference from Example 1 is that the average particle hardness of the first electrode active material sublayer in this positive electrode sheet is 100 MPa, and the average particle hardness of the second electrode active material sublayer is 5100 MPa. The resulting battery is designated as S4.

[0063] Example 5

[0064] The difference from Example 1 is that the average particle hardness of the first electrode active material sublayer in this positive electrode sheet is 175 MPa, the average particle hardness of the second electrode active material sublayer is 275 MPa, and the average particle hardness of the third electrode active material sublayer is 375 MPa. The resulting battery is designated as S5.

[0065] Example 6

[0066] 100g of NCM811, 1g of conductive agent Super P, and 0.5g of binder PVDF5130 were added to NMP and mixed thoroughly to obtain the positive electrode slurry. The preset maximum compaction density of the electrode sheet was 3.6g / cm³. 3 The above-mentioned positive electrode slurry is applied to the surface of the positive electrode current collector (aluminum foil) using a single-layer coating die. After drying, it is wound up for a second coating until the number of coating layers reaches 3. After drying, rolling, and slitting, a positive electrode sheet with 3 sub-layers of electrode active material is obtained. The average particle hardness of the first electrode active material sub-layer in this positive electrode sheet is 175 MPa, the average particle hardness of the second electrode active material sub-layer is 200 MPa, and the average particle hardness of the third electrode active material sub-layer is 225 MPa. The resulting battery is designated as S6.

[0067] Example 7

[0068] NCM811, conductive agent Super P, and binder PVDF5130 were mixed by air jet milling. The mixture was then heated and electrospun into fibers. The electrospun product was hot-pressed to obtain electrode active material sublayers with different hardnesses. The mass ratio of NCM811, Super P, and PVDF5130 in the above mixture was 100:1:0.5. The preset maximum compaction density of the electrode sheet was 3.6 g / cm³.3 The aforementioned electrode active material sublayers are sequentially stacked, hot-pressed, fused, and rolled on the surface of the positive electrode current collector-aluminum foil according to their hardness, and then slit to obtain a positive electrode sheet with three electrode active material sublayers. The average particle hardness of the first electrode active material sublayer in this positive electrode sheet is 175 MPa, the average particle hardness of the second electrode active material sublayer is 200 MPa, and the average particle hardness of the third electrode active material sublayer is 225 MPa. The resulting battery is designated S7.

[0069] Example 8

[0070] 100g of NCM811, 1g of conductive agent Super P, and 0.5g of binder PVDF5130 were added to NMP and mixed thoroughly to obtain the positive electrode slurry. The preset maximum compaction density of the electrode sheet was 3.6g / cm³. 3 The above-mentioned positive electrode slurry was coated onto the surface of aluminum foil using a double-layer coating die. After drying, rolling, and slitting, a positive electrode sheet with two sub-layers of active electrode material was obtained. The average particle hardness of the first sub-layer of active electrode material in this positive electrode sheet was 175 MPa, and the average particle hardness of the second sub-layer of active electrode material was 225 MPa. The resulting battery is designated S8.

[0071] Example 9

[0072] NCM811, conductive agent Super P, and binder PVDF5130 were mixed by air jet milling. The mixture was then heated and electrospun into fibers. The electrospun product was hot-pressed to obtain electrode active material sublayers with different hardnesses. The mass ratio of NCM811, Super P, and PVDF5130 in the above mixture was 100:1:0.5. The preset maximum compaction density of the electrode sheet was 3.65 g / cm³. 3 The aforementioned electrode active material sublayers are sequentially stacked, hot-pressed, fused, and rolled on the surface of the positive electrode current collector-aluminum foil according to their hardness, and then slit to obtain a positive electrode sheet with 10 electrode active material sublayers. The average particle hardness of each electrode active material sublayer, from the 1st to the 10th, is 175 MPa, 180 MPa, 185 MPa, ..., 220 MPa, respectively. The resulting battery is denoted as S9.

[0073] Example 10

[0074] NCM811, conductive agent Super P, and binder PVDF5130 were mixed by air jet milling. The mixture was then heated and electrospun into fibers. The electrospun product was hot-pressed to obtain electrode active material sublayers with different hardnesses. The mass ratio of NCM811, Super P, and PVDF5130 in the above mixture was 100:1:0.5. The preset maximum compaction density of the electrode sheet was 3.65 g / cm³. 3 The aforementioned electrode active material sublayers are sequentially stacked, hot-pressed, fused, and rolled on the surface of the positive electrode current collector-aluminum foil according to their hardness, and then slit to obtain a positive electrode sheet with 10 electrode active material sublayers. The average particle hardness of each electrode active material sublayer, from the 1st to the 10th, is 120 MPa, 140 MPa, 160 MPa, ..., 300 MPa, respectively. The resulting battery is denoted as S10.

[0075] Example 11

[0076] The difference from Example 8 is that the maximum compaction density of the preset electrode sheet is 3.65 g / cm³. 3 The number of electrode active material sublayers in the electrode sheet is 6. The average particle hardness of each electrode active material sublayer, from the 1st to the 6th, is 175 MPa, 195 MPa, 215 MPa, ..., 275 MPa, respectively. The resulting battery is denoted as S11.

[0077] Example 12

[0078] Lithium iron phosphate (LFP), a conductive agent, and a binder PVDF are mixed using an air-jet mill. The mixture is then heated and electrospun into fibers. The electrospun product is hot-pressed to obtain electrode active material sublayers with varying hardness. The mass ratio of LFP, conductive agent, and binder is 90:5:5. The preset maximum compaction density of the electrode sheet is 2.65 g / cm³. 3 The aforementioned electrode active material sublayers are sequentially stacked, hot-pressed, fused, and rolled on the surface of the positive electrode current collector-aluminum foil according to their hardness, and then slit to obtain a positive electrode sheet with 10 electrode active material sublayers. The average particle hardness of each electrode active material sublayer, from the 1st to the 10th, is 175 MPa, 180 MPa, 185 MPa, ..., 220 MPa, respectively. The resulting battery is denoted as S12.

[0079] Example 13

[0080] The difference from Example 10 is that the maximum compaction density of the preset electrode sheet is 2.5 g / cm³. 3The number of electrode active material sublayers in the prepared positive electrode sheet is 3, and the absolute value δ of the hardness difference between any two adjacent electrode active material sublayers is... i Both are 25 MPa. The resulting battery is designated S13.

[0081] Example 14

[0082] (1) Preparation of the negative electrode sheet: 100g of graphite negative electrode active material, 1g of thickener, and 1g of emulsion were added to water in a certain order and mixed evenly to obtain the negative electrode active slurry. The preset maximum compaction density of the electrode sheet was 1.65g / cm³. 3 The above-mentioned positive electrode slurry was applied to the surface of the negative electrode current collector—copper foil—using a three-layer coating die. After drying, rolling, and slitting, a negative electrode sheet with 10 sub-layers of electrode active material was obtained. The average particle hardness of each sub-layer of electrode active material was 300 MPa, 305 MPa, ..., 345 MPa, respectively.

[0083] (2) Preparation of positive electrode sheet: 100g of NCM811, 1g of conductive agent Super P and 0.5g of binder PVDF5130 are added to N-methylpyrrolidone (NMP) and mixed evenly to obtain positive electrode slurry. The above positive electrode slurry is uniformly coated on the surface of the positive current collector - aluminum foil.

[0084] (3) Battery fabrication: The negative electrode obtained in step (1) and the positive electrode obtained in step (2) are alternately stacked with a separator to prepare the battery. The positive and negative electrodes are arranged alternately, and adjacent positive and negative electrodes are separated by a separator to obtain a dry cell. The dry cell is placed in an aluminum-plastic film outer packaging, electrolyte is injected, and then it is vacuum sealed. After being placed at 60°C for 48 hours, it is pressurized at 60°C, repackaged, vented, and capacity tested to obtain a stacked soft-pack full battery with a capacity of 2.2Ah. The prepared battery is designated as S14.

[0085] Example 15

[0086] The difference between Example 13 and Example 12 is that the maximum compaction density of the obtained negative electrode sheet is 1.2 g / cm³. 3 The number of electrode active material sublayers is 3, and the absolute value of the hardness difference between any two adjacent electrode active material sublayers is δ. i Both are 25 MPa. The resulting battery is designated S15.

[0087] Example 16

[0088] The positive electrode sheet prepared in Example 7 and the negative electrode sheet prepared in Example 14 were assembled into a battery S16.

[0089] To highlight the beneficial effects of the embodiments of this application, the following comparative examples are provided.

[0090] Comparative Example 1

[0091] NCM811, a conductive agent, and a binder are mixed using an air-jet mill. The mixture is then heated and electrospun into fibers. The electrospun product is hot-pressed to obtain the active material layer. The preset maximum compaction density of the electrode sheet is 3.65 g / cm³. 3 The mass ratio of NCM811, Super-P, and PVDF5130 is 100:1:0.5. The above active material layers are placed on the positive electrode current collector-aluminum foil and rolled to obtain a positive electrode sheet with one active material sublayer and an average particle hardness of 220 MPa. The resulting battery is designated DS1.

[0092] Comparative Example 2

[0093] NCM811, a conductive agent, and a binder were mixed using an air-jet mill. The mixture was then heated and electrospun into fibers. The electrospun product was hot-pressed to obtain electrode active material sublayers with varying hardness. The mass ratio of NCM811, Super P, and PVDF5130 was 100:1:0.5. The preset maximum compaction density of the electrode sheets was 3.65 g / cm³. 3 The aforementioned electrode active material sublayers are sequentially stacked, hot-pressed, fused, and rolled on a positive electrode current collector-aluminum foil according to their hardness, and then slit to obtain positive electrode sheets with two electrode active material sublayers. The average particle hardness of the first electrode active material sublayer is 10 MPa, and the average particle hardness of the second electrode active material sublayer is 60-10 MPa. The resulting battery is designated DS2.

[0094] Comparative Example 3

[0095] LFP, conductive agent, and binder are mixed using an air-jet milling process. The preset maximum compaction density of the electrode sheet is 2.65 g / cm³. 3 The mixture was heated and electrospun into fibers. The electrospun product was then hot-pressed to obtain an electrode sheet. A positive electrode sheet with one layer and an average particle hardness of 220 MPa was obtained. The resulting battery is designated DS3.

[0096] Comparative Example 4

[0097] LFP, conductive agent, and binder are mixed by air jet milling. The mixture is then heated and electrospun into fibers. The electrospun product is hot-pressed to obtain the electrode sheet. The preset maximum compaction density of the electrode sheet is 2.65 g / cm³. 3A positive electrode with two layers is obtained by stacking, hot-pressing, fusing, and rolling the two electrode layers described above. The average particle hardness of the first electrode active material sublayer is 10 MPa, and the average particle hardness of the second electrode active material sublayer is 60-10 MPa. The resulting battery is designated DS4.

[0098] The parameters of the electrode sheets prepared in the above embodiments and comparative examples are summarized in Table 1.

[0099] Table 1 Summary of parameters of the electrode sheets prepared in each embodiment and comparative example

[0100]

[0101]

[0102] The electrode sheets and batteries prepared in the above embodiments and comparative examples were subjected to electrochemical performance tests, including the following test methods:

[0103] (1) The prepared electrode sheet was rolled with progressively increasing pressure, and the breakage of the electrode active material particles in the electrode sheet was observed and the compaction density of the electrode sheet was measured. Rolling was stopped when the electrode active material particles broke, and the compaction density measured in the previous experiment was taken as the maximum compaction density α of the electrode sheet. The results are summarized in Table 2.

[0104] (2) Battery cycle performance test: 1) Charging: 1 / 3C constant current and constant voltage charging to 4.25V / Cell, cut-off current 0.05C, rest for 30min; 2) Discharging: 1 / 3C constant current to 2.5V / Cell, rest for 30min; 3) Cycle 3 times, record the discharge capacity of the 3rd discharge as the battery's true capacity C0; 4) Charging: 1C with the battery's true capacity C0 as 1C, 1C constant current and constant voltage charging to 4.25V, cut-off current 0.05C; 5) Rest for 30min; 6) Discharging: 1C with the battery's true capacity C0 as 1C, 1C constant current discharging to 2.5V; 7) Rest for 30min; 8) Cycle 500 times from 4) to 7). (Note: Since the positive electrode active material used in Example 8 is LFP, the upper limit voltage is set to 3.8V and the lower limit voltage is 2.0V during the test.) The results of the capacity retention rate after 500 battery cycles and the DC resistance (DCIR) measured under that load are summarized in Table 3.

[0105] (3) Disassemble fully charged batteries S1-S12 and DS1-DS4 to obtain their positive electrode plates. Add a certain amount of electrolyte to the positive electrode plates. After the electrolyte has fully penetrated, prepare a sample and perform differential scanning calorimetry (DSC) testing. The specific test conditions are: in an air atmosphere, the temperature is increased from room temperature at a rate of 5℃ / min, and the thermal decomposition temperature of the electrode plates is measured. The results are summarized in Table 4.

[0106] Table 2 shows the maximum compaction density of the electrode sheets prepared in each embodiment and comparative example.

[0107] Example 1 3.61 Example 2 3.60 Example 3 3.61 Example 4 3.57 Example 5 3.59 Example 6 3.60 Example 7 3.61 Example 8 3.60 Example 9 3.67 Example 10 3.65 Example 11 3.65 Example 12 2.65 Example 13 2.50 Example 14 1.66 Example 15 1.28 Example 16 3.61 (positive electrode) / 1.65 (negative electrode) Comparative Example 1 3.56 Comparative Example 2 3.51 Comparative Example 3 2.57 Comparative Example 4 2.53

[0108] Table 3 shows the capacity retention and DCIR growth rate of the batteries prepared in the examples and comparative examples.

[0109]

[0110]

[0111] Table 4. Thermal decomposition temperatures of the positive electrode sheets disassembled from the batteries of the examples and comparative examples.

[0112]

[0113]

[0114] Combining the data in Tables 2 and 3, it can be seen that, while maintaining the integrity of the electrode active material particles, the maximum compaction density of the electrode active material in the electrode sheets provided in Examples 1-16 of this application is close to the preset maximum compaction density. With the same material, the maximum compaction density of the electrode sheets in the examples is significantly higher than that in the comparative example. Furthermore, the more sublayers of electrode active material in the electrode sheet and the smaller the hardness difference between adjacent sublayers, the greater its maximum compaction density (see Examples 9 and 11). It is important to know that when the maximum compaction density of the electrode sheet is within a suitable range, the greater the maximum compaction density, the greater the energy density of the corresponding battery. When the electrode active materials in the battery are the same, the battery capacity retention rate of the batteries in Examples S1-S16 is higher than that in the comparative example, and the DC internal resistance of the batteries in the examples is relatively smaller. Measurements of the thermal decomposition temperature of the positive electrode sheet revealed that, when using the same electrode active material, the thermal decomposition temperature of the positive electrode sheet prepared in the examples is higher than that in the comparative example, indicating that the positive electrode sheet provided in the examples of this application has better thermal stability and can provide a battery with more stable high-temperature performance and higher safety performance. In particular, S16 and S7 use the same positive electrode, but their thermal decomposition temperatures differ, which is a normal experimental error.

[0115] In summary, the electrode plates of the embodiments of this application can be used to provide batteries with high energy density and long cycle life.

[0116] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. An electrode sheet, characterized in that, The electrode sheet includes a current collector and an electrode active material layer disposed on at least one surface of the current collector; the electrode active material layer includes at least two electrode active material sub-layers, and the electrode active material sub-layers satisfy the following relationship: n×δ i ≤10000,H i -H i-1 ≤5;H i-1 <H i ; 3.65g / cm 3 ≤α<5g / cm 3 ,n≥10; Where n represents the total number of sublayers of the electrode active material, and i is any integer value between 2 and n; H i H1 represents the hardness of the i-th electrode active material sublayer, and H1 represents the hardness of the 1-th electrode active material sublayer, both in MPa; wherein, the 1-th electrode active material sublayer is in contact with the current collector; δ i α represents the absolute value of the hardness difference between the i-th electrode active material sublayer and the (i-1)-th electrode active material sublayer, in MPa; α is the maximum compaction density of the electrode sheet.

2. The electrode sheet according to claim 1, characterized in that, In the electrode sheet, the absolute value of the hardness difference between any two adjacent electrode active material sublayers is equal.

3. The electrode sheet according to claim 1, characterized in that, The electrode active material includes a positive electrode active material; wherein the positive electrode active material includes at least one of lithium nickel cobalt manganese oxygen ternary material, lithium nickel cobalt aluminum oxygen ternary material, and lithium nickel manganese cobalt aluminum oxygen quaternary material.

4. The electrode sheet according to claim 3, characterized in that, The positive electrode active material includes a magnesium-doped multi-component nickel-containing active material, wherein the multi-component nickel-containing active material includes at least one of lithium nickel manganese cobalt oxygen ternary material, lithium nickel cobalt aluminum oxygen ternary material, and lithium nickel manganese cobalt aluminum oxygen quaternary material.

5. The electrode sheet according to claim 4, characterized in that, The mass content of magnesium in the magnesium-doped multi-component nickel-containing active material is greater than 0 and less than 4000 ppm.

6. A lithium battery, characterized in that, The lithium battery has electrode plates as described in any one of claims 1-5.

7. A powered vehicle, characterized in that, The power vehicle has a lithium battery as described in claim 6.

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