Electrode sheet, and lithium-ion battery containing same

Abstract

The present application belongs to the field of lithium-ion batteries. Provided in the present application are an electrode sheet, and a lithium-ion battery containing same. An active layer of the electrode sheet comprises a first layer and a second layer, wherein the first layer is arranged close to a current collector, the second layer is arranged on the side of the first layer that is away from the current collector, and the mass percentage content of a binder of the first layer is greater than that of the second layer. A binder is reallocated, such that the migration of the binder can be improved while ensuring the peel strength and adhesiveness, and the impact of the migration of the binder on the uniformity and the conductivity is reduced, thereby further improving the manufacturability of the electrode sheet and the electrical properties thereof such as the energy density. The present application is very suitable for the adaptation of a lithium manganese iron phosphate cathode having a small particle size and a large specific surface area, and a battery therefor.

Description

Electrode sheet and lithium ion battery containing same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 10, 2024, with application number 202411266532X. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of lithium-ion batteries, and in particular to an electrode sheet and a lithium-ion battery containing the same. Background Art

[0003] Against the backdrop of today's global energy transition, the rapid advancement of new energy technologies has significantly driven the development of battery materials science. Lithium manganese iron phosphate (LMFP), a cathode material with enormous potential, is increasingly gaining attention within the field. LMFP combines the safety, reliability, environmental friendliness, and thermal stability of lithium iron phosphate (LFP) while offering significant improvements in energy density, cost-effectiveness, and cycle life. These properties are crucial for the commercialization of new energy applications such as electric vehicles and large-scale energy storage systems.

[0004] Technical issues

[0005] The commercial application of LMFP materials still faces several challenges. First, LMFP materials generally have a small particle size and a large specific surface area. While this improves reaction activity to a certain extent, it also leads to particle agglomeration and poor dispersion in the cathode slurry. Furthermore, to enhance the interconnectivity between cathode particles, it is usually necessary to increase the amount of cathode binder, such as PVDF. However, a high content of cathode binder occupies space in the active material, limiting the potential for growth in the battery's energy and power density, and hindering the potential application of LMFP materials in high-efficiency batteries.

[0006] In addition, another challenge that often arises in the LMFP battery manufacturing process is that during the baking process of the negative electrode sheet, the commonly used negative electrode binder - styrene butadiene rubber (SBR) - is very easy to float up. This not only weakens the viscosity of the first layer, but also causes the negative electrode conductive agent, such as Super P, to float up, thereby seriously affecting the electrical conductivity and, in turn, the battery's charge and discharge efficiency and cycle life.

[0007] Therefore, it is necessary to optimize and improve the solution for lithium-ion battery electrode sheets to improve the above-mentioned deficiencies and effectively promote the manufacture and application of high-performance lithium manganese iron phosphate batteries.

[0008] Technical Solutions

[0009] The present application provides an electrode sheet and a lithium-ion battery containing the same, wherein the active layer of the electrode sheet includes a first layer and a second layer, wherein the first layer is arranged close to the current collector, and the second layer is arranged on the side of the first layer away from the current collector, and the mass percentage of the binder in the first layer is greater than that in the second layer. By redistributing the binder, the peeling force and adhesion are ensured while the migration of the binder can be improved, and the influence of the binder migration on the uniformity and conductivity can be reduced, thereby improving the manufacturability of the electrode sheet and electrical properties such as energy density. The electrode sheet is very suitable for lithium manganese iron phosphate positive electrodes with small particle size and large specific surface area and the adaptation of batteries thereof.

[0010] In a first aspect, the present application provides an electrode sheet comprising a current collector and an active layer arranged on the current collector, the active layer comprising a first layer and a second layer, wherein the first layer is arranged close to the current collector, and the second layer is arranged on a side of the first layer away from the current collector, wherein the mass percentage of the binder in the first layer is greater than the mass percentage of the binder in the second layer.

[0011] In a second aspect, the present application provides a lithium-ion battery comprising the electrode sheet described in the first aspect.

[0012] Beneficial effects

[0013] Compared with the related technical solutions, this application has at least the following beneficial effects:

[0014] This application divides the active layer into two layers, an upper layer and an lower layer, and increases the mass percentage of the binder in the first layer close to the current collector to increase the peeling force and adhesion in the electrode process, thereby solving the defect of edge powder falling and increasing the peeling force during coating and cold pressing by more than 2 times; it can also improve the migration of the binder, so that the uniformity of the redistribution of the binder after migration (floating) to the second layer is improved, and the influence of the migration of the binder on the adhesion and the distribution of the conductive agent is alleviated, thereby improving the conductivity and effectively reducing the internal resistance; at the same time, due to the existence of the first layer, the mass percentage of the binder in the second layer is reduced, and the total amount of binder used in the active layer is reduced, thereby providing more space for the active material and fully improving the energy density.

[0015] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 is a structural diagram of an electrode sheet in one embodiment of the present application.

[0017] Among them, 1-current collector, 2-first layer, 3-second layer.

[0018] Modes for Carrying Out the Invention

[0019] In a first aspect, the present application provides an electrode sheet comprising a current collector and an active layer arranged on the current collector, the active layer comprising a first layer and a second layer, wherein the first layer is arranged close to the current collector, and the second layer is arranged on a side of the first layer away from the current collector, wherein the mass percentage of the binder in the first layer is greater than the mass percentage of the binder in the second layer.

[0020] The present application solves the defect of edge powder falling by increasing the mass percentage of the binder in the first layer close to the current collector to increase the peeling force and adhesion in the electrode process, and can increase the peeling force during coating and cold pressing by more than 2 times; it can also improve the migration of the binder, so that the uniformity of the redistribution of the binder after migration (floating) to the second layer is improved, and the influence of the migration of the binder on the adhesion and the distribution of the conductive agent is alleviated, thereby improving the conductivity and effectively reducing the internal resistance; at the same time, due to the existence of the first layer, the mass percentage of the binder in the second layer is reduced, and the total amount of binder used in the active layer is reduced, thereby providing more space for the active material and fully improving the energy density.

[0021] In one embodiment, the structure of the electrode sheet is as shown in Figure 1, and the electrode sheet includes a current collector 1 and an active layer arranged on the current collector 1, and the active layer includes a first layer 2 and a second layer 3, wherein the first layer 2 is arranged close to the current collector, and the second layer 3 is arranged on the side of the first layer 2 away from the current collector, wherein the mass percentage of the binder in the first layer 2 is greater than the mass percentage of the binder in the second layer 3.

[0022] The following are optional technical solutions for this application, but are not intended to limit the technical solutions provided in this application. Through the following technical solutions, the technical objectives and beneficial effects of this application can be better achieved and realized.

[0023] As an optional technical solution of the present application, when the electrode sheet is a positive electrode, the active layer includes a positive electrode active material, a positive electrode conductor and a positive electrode binder.

[0024] Optionally, the positive electrode active material includes lithium manganese iron phosphate.

[0025] The electrode sheet scheme described in this application is very suitable for lithium manganese iron phosphate positive electrodes with small particle size and large specific surface area. It can give full play to its energy density advantages and potential to obtain positive electrode sheets with better electrical performance.

[0026] Optionally, the positive electrode binder includes PVDF.

[0027] As an optional technical solution of the present application, based on the mass of the active layer of the positive electrode as 100%, the total mass percentage of the positive electrode binder is 0.1%~2%, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, etc., and can be optionally 0.5%~1.8%, and further optionally 1.2%~1.6%.

[0028] In related technologies, the total mass percentage of the binder in the active layer is generally 3% to 4%. The electrode sheet solution described in this application can not only ensure sufficient adhesion between the particles and high peeling force of the active layer, but also effectively reduce the total amount of binder used.

[0029] Optionally, based on the mass of the positive electrode active layer as 100%, the total mass percentage of the positive electrode active material is 96% to 98%, for example, 96%, 96.2%, 96.4%, 96.6%, 96.8%, 97%, 97.2%, 97.4%, 97.6%, 97.8%, or 98%, etc.; the total mass percentage of the positive electrode binder is 0.5% to 1.8%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, or 1.8%, etc.; the total mass percentage of the positive electrode conductive agent is 0.2% to 3.5%, for example, 0.2%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, or 3.5%, etc.

[0030] As an optional technical solution of the present application, in the active layer of the positive electrode, the mass percentage of the positive electrode binder of the first layer is 1.1 to 2.5 times the mass percentage of the positive electrode binder of the second layer, for example, 1.1 times, 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2 times, 2.1 times, 2.2 times, 2.3 times, 2.4 times or 2.5 times, etc.

[0031] In this application, the difference in adhesive content between the first layer and the second layer is too large, which not only easily leads to the loss of adhesion and peeling force of the second layer, and affects the energy density and electrical properties of the first layer, but also causes the viscosity of the slurry of the first layer to increase sharply, thereby affecting the electrode manufacturing process.

[0032] As an optional technical solution of the present application, when the electrode sheet is a negative electrode, the active layer includes a negative electrode active material, a negative electrode conductive agent and a negative electrode binder.

[0033] Optionally, the negative electrode binder includes SBR.

[0034] During the baking process of the negative electrode sheet, the SBR binder is more likely to float up. Therefore, the present application further optionally stipulates that in the negative electrode, the mass percentage of the SBR in the first layer is greater than the mass percentage of the SBR in the second layer, so that during the drying process of the negative electrode sheet, the SBR in the first layer floats up, driving the SP to float up, so that the conductive agent and binder are evenly distributed inside the entire negative electrode sheet.

[0035] As an optional technical solution of the present application, based on the mass of the active layer of the negative electrode as 100%, the total mass percentage of the negative electrode binder is 0.1% to 4%, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8% or 4%, etc.

[0036] Optionally, based on the mass of the negative electrode active layer as 100%, the total mass percentage of the negative electrode active material is 95% to 99%, for example, 95%, 95.2%, 95.4%, 95.6%, 95.8%, 96%, 96.2%, 96.4%, 96.6%, 96.8%, 97%, 97.2%, 97.4%, 97.6%, 97.8% or 98%, etc.; the total mass percentage of the negative electrode binder is 0.8% to 3%, for example, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8% or 3%, etc.; the total mass percentage of the negative electrode conductor is 0.2% to 2%, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, etc.

[0037] As an optional technical solution of the present application, in the active layer of the negative electrode, the mass percentage of the negative electrode binder of the first layer is 1.1 to 5 times the mass percentage of the negative electrode binder of the second layer, for example, 1.1 times, 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2 times, 2.1 times, 2.2 times, 2.3 times, 2.4 times, 2.5 times, 2.8 times, 3 times, 3.3 times, 3.5 times, 3.8 times, 4 times, 4.3 times, 4.5 times, 4.8 times or 5 times, etc.

[0038] As an optional technical solution of the present application, in the active layer of the negative electrode, the mass percentage of the negative electrode conductive agent in the first layer is 1.1 to 5 times the mass percentage of the negative electrode conductive agent in the second layer, for example, 1.1 times, 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2 times, 2.1 times, 2.2 times, 2.3 times, 2.4 times, 2.5 times, 2.8 times, 3 times, 3.3 times, 3.5 times, 3.8 times, 4 times, 4.3 times, 4.5 times, 4.8 times or 5 times, etc.

[0039] In a second aspect, the present application provides a lithium-ion battery comprising the electrode sheet described in the first aspect.

[0040] As an optional technical solution of the present application, the lithium-ion battery includes a lithium iron manganese phosphate battery, and the positive electrode and the negative electrode of the lithium iron manganese phosphate battery are both the electrode sheets.

[0041] Due to space limitations and to avoid redundancy, this application does not list all point values ​​within the above numerical range one by one, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0042] The technical solution of this application is further explained below through specific implementation methods.

[0043] Those skilled in the art should understand that the embodiments are only intended to help understand the present application and should not be regarded as specific limitations of the present application.

[0044] Example 1

[0045] This embodiment provides an electrode sheet:

[0046] The electrode sheet is a positive electrode, comprising a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode first layer and a positive electrode second layer, wherein the positive electrode first layer is disposed on the positive electrode current collector, and the positive electrode second layer is disposed on a side of the positive electrode first layer away from the positive electrode current collector;

[0047] Based on 100% by mass of the positive electrode active layer, the positive electrode active layer includes 96.9% of a positive electrode active material, lithium manganese iron phosphate, 1.1% of a positive electrode conductive agent (Super P and CNT in a mass ratio of 1:1), and 2% of a positive electrode binder, PVDF;

[0048] Based on the mass of the positive electrode second layer being 100%, the positive electrode second layer comprises 97.7% of the positive electrode active material lithium manganese iron phosphate, 1.1% of the positive electrode conductive agent (Super P and CNT with a mass ratio of 1:1), and 1.2% of the positive electrode binder PVDF;

[0049] Based on the mass of the positive electrode first layer being 100%, the positive electrode first layer comprises 96.1% of the positive electrode active material lithium manganese iron phosphate, 1.1% of the positive electrode conductive agent (Super P and CNT with a mass ratio of 1:1), and 2.8% of the positive electrode binder PVDF;

[0050] In the positive electrode active layer, the ratio of the mass percentage of the positive electrode binder in the first positive electrode layer to the mass percentage of the positive electrode binder in the second positive electrode layer is 2.33:1.

[0051] Example 2

[0052] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is changed, while the mass percentage ratio of the positive electrode binder in the first positive electrode layer to the second positive electrode layer is maintained at 2.33:1, that is:

[0053] Based on 100% by mass of the positive electrode active layer, the positive electrode active layer includes 97.2% of a positive electrode active material, 1.1% of a positive electrode conductor, and 1.7% of a positive electrode binder;

[0054] Based on 100% by mass of the positive electrode second layer, the positive electrode second layer includes 97.88% of a positive electrode active material, 1.1% of a positive electrode conductor, and 1.02% of a positive electrode binder;

[0055] Based on 100% by mass of the positive electrode first layer, the positive electrode first layer includes 96.52% of a positive electrode active material, 1.1% of a positive electrode conductor, and 2.38% of a positive electrode binder;

[0056] Except for the above, other conditions are exactly the same as those in Example 1.

[0057] Example 3

[0058] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is changed, while the mass percentage ratio of the positive electrode binder in the first positive electrode layer to the second positive electrode layer is maintained at 2.33:1, that is:

[0059] Based on 100% by mass of the positive electrode active layer, the positive electrode active layer includes 97.5% of a positive electrode active material, 1.1% of a positive electrode conductor, and 1.4% of a positive electrode binder;

[0060] Based on 100% by mass of the positive electrode second layer, the positive electrode second layer includes 98.06% of a positive electrode active material, 1.1% of a positive electrode conductor, and 0.84% ​​of a positive electrode binder;

[0061] Based on 100% by mass of the positive electrode first layer, the positive electrode first layer includes 96.94% of a positive electrode active material, 1.1% of a positive electrode conductor, and 1.96% of a positive electrode binder;

[0062] Except for the above, other conditions are exactly the same as those in Example 1.

[0063] Example 4

[0064] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is changed, while the mass percentage ratio of the positive electrode binder in the first positive electrode layer to the second positive electrode layer is maintained at 2.33:1, that is:

[0065] Based on 100% by mass of the positive electrode active layer, the positive electrode active layer includes 96.6% of a positive electrode active material, 1.1% of a positive electrode conductor, and 2.3% of a positive electrode binder;

[0066] Based on 100% by mass of the positive electrode second layer, the positive electrode second layer includes 97.52% of a positive electrode active material, 1.1% of a positive electrode conductor, and 1.38% of a positive electrode binder;

[0067] Based on 100% by mass of the positive electrode first layer, the positive electrode first layer includes 95.68% of a positive electrode active material, 1.1% of a positive electrode conductor, and 3.22% of a positive electrode binder;

[0068] Except for the above, other conditions are exactly the same as those in Example 1.

[0069] Example 5

[0070] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is kept unchanged, and the mass percentage ratio of the positive electrode binder in the first positive electrode layer to that in the second positive electrode layer is changed to 1.1:1, that is:

[0071] Based on 100% by mass of the positive electrode second layer, the positive electrode second layer includes 97% of a positive electrode active material, 1.1% of a positive electrode conductor, and 1.9% of a positive electrode binder;

[0072] Based on 100% by mass of the positive electrode first layer, the positive electrode first layer includes 96.8% of a positive electrode active material, 1.1% of a positive electrode conductor, and 2.1% of a positive electrode binder;

[0073] Except for the above, other conditions are exactly the same as those in Example 1.

[0074] Example 6

[0075] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is kept unchanged, and the mass percentage ratio of the positive electrode binder in the first positive electrode layer to that in the second positive electrode layer is changed to 2.5:1, that is:

[0076] Based on 100% by mass of the positive electrode second layer, the positive electrode second layer includes 97.76% of a positive electrode active material, 1.1% of a positive electrode conductor, and 1.14% of a positive electrode binder;

[0077] Based on 100% by mass of the positive electrode first layer, the positive electrode first layer includes 96.04% of a positive electrode active material, 1.1% of a positive electrode conductor, and 2.86% of a positive electrode binder;

[0078] Except for the above, other conditions are exactly the same as those in Example 1.

[0079] Example 7

[0080] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is kept unchanged, and the mass percentage ratio of the positive electrode binder in the first positive electrode layer to that in the second positive electrode layer is changed to 2.8:1, that is:

[0081] Based on 100% by mass of the positive electrode second layer, the positive electrode second layer includes 97.85% of a positive electrode active material, 1.1% of a positive electrode conductor, and 1.05% of a positive electrode binder;

[0082] Based on 100% by mass of the positive electrode first layer, the positive electrode first layer includes 95.95% of a positive electrode active material, 1.1% of a positive electrode conductor, and 2.95% of a positive electrode binder;

[0083] Except for the above, other conditions are exactly the same as those in Example 1.

[0084] Example 8

[0085] This embodiment provides an electrode sheet:

[0086] The electrode sheet is a negative electrode, comprising a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector, wherein the negative electrode active layer comprises a negative electrode first layer and a negative electrode second layer, wherein the negative electrode first layer is disposed on the negative electrode current collector, and the negative electrode second layer is disposed on a side of the negative electrode first layer away from the negative electrode current collector;

[0087] Based on 100% by mass of the negative electrode active layer, the negative electrode active layer includes 96.7% of negative electrode active material graphite, 0.6% of negative electrode conductive agent Super P, and 2.7% of negative electrode binder (1.5% of SBR and 1.2% of CMC);

[0088] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 97.96% of negative electrode active material graphite, 0.24% of negative electrode conductive agent Super P, and 1.8% of negative electrode binder (0.6% of SBR and 1.2% of CMC);

[0089] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 95.44% of negative electrode active material graphite, 0.96% of negative electrode conductive agent Super P, and 3.6% of negative electrode binder (2.4% of SBR and 1.2% of CMC);

[0090] In the negative electrode active layer, the ratio of the mass percentage of the negative electrode binder in the first negative electrode layer to the mass percentage of the negative electrode binder in the second negative electrode layer is 2:1; the ratio of the mass percentage of the negative electrode binder SBR in the first negative electrode layer to the mass percentage of the negative electrode binder SBR in the second negative electrode layer is 4:1; and the ratio of the mass percentage of the negative electrode conductive agent in the first negative electrode layer to the mass percentage of the negative electrode conductive agent in the second negative electrode layer is 4:1.

[0091] Example 9

[0092] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is changed, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is maintained at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the negative electrode conductive agent in the second negative electrode layer is maintained at 4:1, that is:

[0093] Based on 100% by mass of the negative electrode active layer, the negative electrode active layer includes 97.3% of negative electrode active material graphite, 0.6% of negative electrode conductive agent Super P, and 2.1% of negative electrode binder (1.17% of SBR and 0.93% of CMC);

[0094] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 98.36% of negative electrode active material graphite, 0.24% of negative electrode conductive agent Super P, and 1.4% of negative electrode binder (0.47% of SBR and 0.93% of CMC);

[0095] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 96.24% of negative electrode active material graphite, 0.96% of negative electrode conductive agent Super P, and 2.8% of negative electrode binder (1.87% of SBR and 0.93% of CMC);

[0096] Except for the above, other conditions are exactly the same as those in Example 8.

[0097] Example 10

[0098] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is changed, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is maintained at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the negative electrode conductive agent in the second negative electrode layer is maintained at 4:1, that is:

[0099] Based on 100% by mass of the negative electrode active layer, the negative electrode active layer includes 96.1% of negative electrode active material graphite, 0.6% of negative electrode conductive agent Super P, and 3.3% of negative electrode binder (1.83% of SBR and 1.47% of CMC);

[0100] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 97.56% of negative electrode active material graphite, 0.24% of negative electrode conductive agent Super P, and 2.2% of negative electrode binder (0.73% of SBR and 1.47% of CMC);

[0101] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 94.64% of negative electrode active material graphite, 0.96% of negative electrode conductive agent Super P, and 4.4% of negative electrode binder (2.93% of SBR and 1.47% of CMC);

[0102] Except for the above, other conditions are exactly the same as those in Example 8.

[0103] Example 11

[0104] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is maintained unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is maintained at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is changed to 0.88:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, that is:

[0105] Based on the mass of the negative electrode second layer being 100%, 1.8% of the negative electrode binder in the negative electrode second layer is composed of 1.6% of SBR and 0.2% of CMC;

[0106] Based on the mass of the negative electrode first layer being 100%, 3.6% of the negative electrode binder in the negative electrode first layer is composed of 1.4% of SBR and 2.2% of CMC;

[0107] Except for the above, other conditions are exactly the same as those in Example 8.

[0108] Example 12

[0109] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is maintained unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is maintained at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is changed to 1.14:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, that is:

[0110] Based on the mass of the negative electrode second layer being 100%, 1.8% of the negative electrode binder in the negative electrode second layer is composed of 1.4% of SBR and 0.4% of CMC;

[0111] Based on the mass of the negative electrode first layer being 100%, 3.6% of the negative electrode binder in the negative electrode first layer is composed of 1.6% of SBR and 2% of CMC;

[0112] Except for the above, other conditions are exactly the same as those in Example 8.

[0113] Example 13

[0114] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is maintained unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is maintained at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is changed to 2:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, that is:

[0115] Based on the mass of the negative electrode second layer being 100%, 1.8% of the negative electrode binder in the negative electrode second layer is composed of 1% SBR and 0.8% CMC;

[0116] Based on the mass of the negative electrode first layer being 100%, 3.6% of the negative electrode binder in the negative electrode first layer is composed of 2% of SBR and 1.6% of CMC;

[0117] Except for the above, other conditions are exactly the same as those in Example 8.

[0118] Example 14

[0119] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is maintained unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is maintained at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is changed to 5:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, that is:

[0120] Based on the mass of the negative electrode second layer being 100%, 1.8% of the negative electrode binder in the negative electrode second layer is composed of 0.5% of SBR and 1.3% of CMC;

[0121] Based on the mass of the negative electrode first layer being 100%, 3.6% of the negative electrode binder in the negative electrode first layer is composed of 2.5% of SBR and 1.1% of CMC;

[0122] Except for the above, other conditions are exactly the same as those in Example 8.

[0123] Example 15

[0124] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is maintained unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is changed to 1.1:1, but the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, that is:

[0125] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 97.19% of negative electrode active material graphite, 0.24% of negative electrode conductive agent Super P, and 2.57% of negative electrode binder (0.6% of SBR and 1.97% of CMC);

[0126] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 96.21% of negative electrode active material graphite, 0.96% of negative electrode conductive agent Super P, and 2.83% of negative electrode binder (2.4% of SBR and 0.43% of CMC);

[0127] Except for the above, other conditions are exactly the same as those in Example 8.

[0128] Example 16

[0129] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is maintained unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is changed to 4:1, but the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, that is:

[0130] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 98.68% of negative electrode active material graphite, 0.24% of negative electrode conductive agent Super P, and 1.08% of negative electrode binder (0.6% of SBR and 0.48% of CMC);

[0131] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 94.72% of negative electrode active material graphite, 0.96% of negative electrode conductive agent Super P, and 4.32% of negative electrode binder (2.4% of SBR and 1.92% of CMC);

[0132] Except for the above, other conditions are exactly the same as those in Example 8.

[0133] Example 17

[0134] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is maintained unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is changed to 5:1, but the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, that is:

[0135] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 98.86% of negative electrode active material graphite, 0.24% of negative electrode conductive agent Super P, and 0.9% of negative electrode binder (0.6% of SBR and 0.3% of CMC);

[0136] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 94.54% of negative electrode active material graphite, 0.96% of negative electrode conductive agent Super P, and 4.5% of negative electrode binder (2.4% of SBR and 2.1% of CMC);

[0137] Except for the above, other conditions are exactly the same as those in Example 8.

[0138] Example 18

[0139] This embodiment provides an electrode sheet, in which the total mass percentage of the negative electrode binder is maintained unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer to the second negative electrode layer is maintained at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer to the second negative electrode layer is maintained at 4:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer to the second negative electrode layer is changed to 1:1, that is:

[0140] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 97.6% of negative electrode active material graphite, 0.6% of negative electrode conductive agent Super P, and 1.8% of negative electrode binder (0.6% of SBR and 1.2% of CMC);

[0141] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 95.8% of negative electrode active material graphite, 0.6% of negative electrode conductive agent Super P, and 3.6% of negative electrode binder (2.4% of SBR and 1.2% of CMC);

[0142] Except for the above, other conditions are exactly the same as those in Example 8.

[0143] Comparative Example 1

[0144] This comparative example provides an electrode sheet, wherein the positive electrode active layer of the electrode sheet is not delaminated, that is:

[0145] The electrode sheet is a positive electrode, including a positive electrode current collector and a positive electrode active layer arranged on the positive electrode current collector. Based on the mass of the positive electrode active layer as 100%, the positive electrode active layer includes 96.9% of the positive electrode active material lithium manganese iron phosphate, 1.1% of the positive electrode conductive agent (Super P and CNT with a mass ratio of 1:1), and 2% of the positive electrode binder PVDF.

[0146] Comparative Example 2

[0147] This comparative example provides an electrode sheet, wherein the positive electrode active layer of the electrode sheet is not delaminated, that is:

[0148] The electrode sheet is a negative electrode, including a negative electrode current collector and a negative electrode active layer arranged on the negative electrode current collector. Taking the mass of the negative electrode active layer as 100%, the negative electrode active layer includes 96.7% of negative electrode active material graphite, 0.6% of negative electrode conductive agent Super P, and 2.7% of negative electrode binder (1.5% SBR and 1.2% CMC).

[0149] Comparative Example 3

[0150] This comparative example provides an electrode sheet, in which the total mass percentage of the negative electrode binder is kept unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer and the second negative electrode layer is changed to 1:1, the mass percentage ratio of the SBR in the first negative electrode layer and the second negative electrode layer is changed to 1:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer and the second negative electrode layer is changed to 4:1, that is:

[0151] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 97.06% of negative electrode active material graphite, 0.24% of negative electrode conductive agent Super P, and 2.7% of negative electrode binder (1.5% of SBR and 1.2% of CMC);

[0152] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 96.34% of negative electrode active material graphite, 0.96% of negative electrode conductive agent Super P, and 2.7% of negative electrode binder (1.5% of SBR and 1.2% of CMC);

[0153] Except for the above, other conditions are exactly the same as those in Example 8.

[0154] Comparative Example 4

[0155] This comparative example provides an electrode sheet, in which the total mass percentage of the negative electrode binder is kept unchanged, the mass percentage ratio of the negative electrode binder in the first negative electrode layer and the second negative electrode layer is changed to 1:1, the mass percentage ratio of the SBR in the first negative electrode layer and the second negative electrode layer is changed to 4:1, and the mass percentage ratio of the negative electrode conductive agent in the first negative electrode layer and the second negative electrode layer is changed to 4:1, that is:

[0156] Based on the mass of the negative electrode second layer being 100%, the negative electrode second layer comprises 97.06% of negative electrode active material graphite, 0.24% of negative electrode conductive agent Super P, and 2.7% of negative electrode binder (0.6% of SBR and 2.1% of CMC);

[0157] Based on the mass of the negative electrode first layer being 100%, the negative electrode first layer comprises 96.34% of negative electrode active material graphite, 0.96% of negative electrode conductive agent Super P, and 2.7% of negative electrode binder (2.4% of SBR and 0.3% of CMC);

[0158] Except for the above, other conditions are exactly the same as those in Example 8.

[0159] Characterization and testing:

[0160] Ⅰ. Peel force test:

[0161] The electrode sheets of Examples 1-7 and Comparative Example 1 were all manufactured using the same positive electrode manufacturing process. Similarly, the electrode sheets of Examples 8-18 and Comparative Examples 2-4 were all manufactured using the same negative electrode manufacturing process.

[0162] The coating peeling force and cold pressing peeling force of the electrode sheets obtained in Examples 1-18 and Comparative Examples 1-4 were tested during the manufacturing process, and the results are listed in Table 1.

[0163] Table 1

[0164]

[0165] The results show that the electrode peel force is proportional to the binder content at the current collector contact point. The higher the binder content in the first layer, the higher the coating peel force, and the correspondingly higher the peel force after cold pressing. The negative electrode CMC content has little to do with the peel force, which is instead determined by the SBR content.

[0166] II. Select the electrode sheet provided in any one of Examples 1-7 and Comparative Example 1 as the positive electrode, and select the electrode sheet provided in any one of Examples 8-18 and Comparative Examples 2-4 as the negative electrode for assembly. The positive electrode, polyethylene separator, and negative electrode are stacked. The battery is then assembled, followed by lamination, drying, electrolyte injection (the electrolyte is 1 mol / L LiPF6 in ethyl carbonate (EC) + dimethyl carbonate (DMC), with an additive weight percentage of 2% fluoroethylene carbonate (FEC)), packaging, and formation to constant volume to produce a lithium iron manganese phosphate battery.

[0167] The obtained battery was tested, including the DC internal resistance (DCR) of the battery cell and the capacity decay percentage after 500 cycles (test conditions: 25°C, 2C constant current charge, 1C constant current discharge). The results are recorded in Table 2.

[0168] Table 2

[0169]

[0170] As shown in Table 2, cells assembled with positive electrode examples 2-4 and negative electrode example 8 demonstrate that increasing the binder content in the positive electrode solution did not reduce the internal resistance of the cell, but did reduce cycle degradation. Increasing the total binder content resulted in a tighter bond between the positive electrode active material and the current collector during cell cycling, maintaining consistent conductivity with increasing cycle count. Positive electrode examples 5-7 demonstrate that, because the negative electrode's electrons concentrate at the point of contact between the first layer and the current collector during charge and discharge, a higher SBR content in the first layer resulted in a more pronounced effect.

[0171] The negative electrode example shows that as the conductive agent content in the first layer increases, the internal resistance of the cell decreases. Changes in the binder do not affect the internal resistance. However, the negative electrode's cycling performance is the result of the combined effects of the conductive and binder agents. Lower internal resistance, i.e., higher conductive agent content in the first layer, leads to better cycling performance; higher binder content in the first layer also leads to better cycling performance. Compared to Comparative Examples 1 and 2, the internal resistance and cycling performance of the cell with the layered components are significantly superior to those of the unlayered, uniform electrode.

Claims

1. An electrode sheet comprising a current collector and an active layer disposed on the current collector, wherein the active layer comprises a first layer and a second layer, wherein: The first layer is arranged close to the current collector, and the second layer is arranged on a side of the first layer away from the current collector, wherein the mass percentage of the binder in the first layer is greater than the mass percentage of the binder in the second layer.

2. The electrode sheet according to claim 1, wherein When the electrode sheet is a positive electrode, the active layer includes a positive electrode active material, a positive electrode conductor and a positive electrode binder.

3. The electrode sheet according to claim 2, wherein: The positive electrode active material includes lithium manganese iron phosphate.

4. The electrode sheet according to claim 2 or 3, wherein: The positive electrode binder includes PVDF.

5. The electrode sheet according to any one of claims 2 to 4, wherein: Based on the mass of the active layer of the positive electrode being 100%, the total mass percentage of the positive electrode binder is 0.1% to 2%.

6. The electrode sheet according to any one of claims 2 to 5, wherein: Based on the mass of the positive electrode active layer as 100%, the total mass percentage of the positive electrode active material is 96%-98%, the total mass percentage of the positive electrode binder is 0.5%-1.8%, and the total mass percentage of the positive electrode conductive agent is 0.2%-3.5%.

7. The electrode sheet according to any one of claims 2 to 6, wherein: In the active layer of the positive electrode, the mass percentage of the positive electrode binder in the first layer is 1.1 to 2.5 times the mass percentage of the positive electrode binder in the second layer.

8. The electrode sheet according to any one of claims 1 to 7, wherein: When the electrode sheet is a negative electrode, the active layer includes a negative electrode active material, a negative electrode conductive agent and a negative electrode binder.

9. The electrode sheet according to claim 8, wherein The negative electrode binder includes SBR.

10. The electrode sheet according to claim 8 or 9, wherein: Based on the mass of the active layer of the negative electrode being 100%, the total mass percentage of the negative electrode binder is 0.1% to 4%.

11. The electrode sheet according to any one of claims 8 to 10, wherein: Based on the mass of the negative electrode active layer as 100%, the total mass percentage of the negative electrode active material is 95%-99%, the total mass percentage of the negative electrode binder is 0.8%-3%, and the total mass percentage of the negative electrode conductive agent is 0.2%-2%.

12. The electrode sheet according to any one of claims 8 to 11, wherein: In the active layer of the negative electrode, the mass percentage of the negative electrode binder in the first layer is 1.1 to 5 times the mass percentage of the negative electrode binder in the second layer.

13. The electrode sheet according to any one of claims 8 to 12, wherein: In the active layer of the negative electrode, the mass percentage of the negative electrode conductive agent in the first layer is 1.1 to 5 times the mass percentage of the negative electrode conductive agent in the second layer.

14. A lithium ion battery, wherein: The electrode sheet comprises the electrode sheet according to any one of claims 1 to 13.

15. The lithium ion battery according to claim 14, wherein The lithium-ion battery includes a lithium iron manganese phosphate battery, and the positive electrode and the negative electrode of the lithium iron manganese phosphate battery are both the electrode sheets.

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