Electrode plate and lithium ion battery comprising same

Abstract

The invention belongs to the field of lithium ion batteries. The invention provides an electrode plate and a lithium ion battery containing the same, an active layer of the electrode plate comprises a first layer and a second layer, the first layer is arranged close to a current collector, the second layer is arranged on one side, far away from the current collector, of the first layer, the mass percentage content of a binder of the first layer is greater than that of the second layer, and the mass percentage content of the binder of the second layer is less than that of the first layer. The adhesive is redistributed, so that release force and cohesiveness are guaranteed, migration of the adhesive can be improved, influence of migration of the adhesive on uniformity and conductivity is reduced, and electrical properties such as manufacturability and energy density of the electrode plate are improved. And the method is very suitable for the adaptation of the lithium manganese iron phosphate positive electrode with small particle size and large specific surface area and the battery thereof.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion batteries and relates to an electrode sheet and a lithium ion battery containing the electrode sheet. Background Art

[0002] In the context of today's global energy transformation, the rapid progress of new energy technologies has greatly promoted the development of battery material science. Lithium manganese iron phosphate (LMPF) is a cathode material with great potential and is gradually becoming the focus of attention in the field. LMPF combines the advantages of lithium iron phosphate (LFP) such as safety, reliability, environmental friendliness, and strong thermal stability, while significantly improving energy density, cost-effectiveness, and cycle life. These characteristics are crucial to promoting the commercialization of new energy applications such as electric vehicles and large-scale energy storage systems.

[0003] However, the commercial application of LMPF materials still faces some challenges. First, the particle size of LMPF materials is generally small and the specific surface area is large. Although this is beneficial to improve the reaction activity to a certain extent, it also causes the particles in the positive electrode slurry to be easy to agglomerate and have poor dispersion. At the same time, in order to enhance the interconnection between the positive electrode particles, it is usually necessary to increase the amount of positive electrode binder, such as PVDF. However, the high content of positive electrode binder occupies the space of active materials, limits the growth space of the battery's energy density and power density, and hinders the application potential of LMPF materials in high-efficiency batteries.

[0004] In addition, another common problem in the LMPF battery manufacturing process is that during the baking process of the negative electrode plate, the commonly used negative electrode binder, styrene-butadiene rubber (SBR), is prone to floating. This not only weakens the viscosity of the first layer, but also causes the negative electrode conductive agent, such as SuperP, to float, thereby seriously affecting the electrical conductivity, and further affecting the battery's charge and discharge efficiency and cycle life.

[0005] Therefore, it is necessary to optimize and improve the solution for lithium-ion battery electrode sheets to solve the above problems and effectively promote the manufacturing and application of high-performance lithium manganese iron phosphate batteries. Summary of the invention

[0006] In view of the problems existing in the prior art, the object of the present invention is to provide 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 the electrical properties such as energy density, and the electrode sheet is very suitable for the adaptation of lithium iron manganese phosphate positive electrodes and batteries with small particle size and large specific surface area.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention 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.

[0009] The present invention can solve the problem 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 the binder in the active layer is reduced, thereby providing more space for the active material and fully improving the energy density.

[0010] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0011] As a preferred technical solution of the present invention, when the electrode sheet is a positive electrode, the active layer includes a positive electrode active material, a positive electrode conductive agent and a positive electrode binder.

[0012] Preferably, the positive electrode active material includes lithium manganese iron phosphate.

[0013] The electrode sheet scheme of the present invention is very suitable for lithium manganese iron phosphate positive electrodes with small particle size and large specific surface area, and can give full play to its advantages and potentials in energy density to obtain positive electrode sheets with better electrical performance.

[0014] Preferably, the positive electrode binder comprises PVDF.

[0015] As a preferred technical solution of the present invention, 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% to 2%, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, etc., preferably 0.5% to 1.8%, and more preferably 1.2% to 1.6%.

[0016] In the prior art, the total mass percentage of the binder in the active layer is generally 3% to 4%. The electrode sheet scheme described in the present invention can not only ensure sufficient adhesion between particles and high peeling force of the active layer, but also effectively reduce the total amount of binder used.

[0017] Preferably, based on the mass of the active layer of the positive electrode 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 conductor 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.

[0018] As a preferred technical solution of the present invention, 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 the mass percentage of the positive electrode binder of the second layer.

[0019] In the present invention, the difference in binder content between the first layer and the second layer is too large, which not only easily leads to 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 a sharp increase in the viscosity of the slurry of the first layer, thereby affecting the electrode manufacturing process.

[0020] As a preferred technical solution of the present invention, 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.

[0021] Preferably, the negative electrode binder comprises SBR.

[0022] During the baking process of the negative electrode sheet, the SBR binder is more likely to float. Therefore, the present invention further prefers 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, driving the SP to float, so that the conductive agent and the binder are evenly distributed inside the entire negative electrode sheet.

[0023] As a preferred technical solution of the present invention, 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.

[0024] Preferably, based on the mass of the active layer of the negative electrode 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%; the negative electrode binder The total mass percentage 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 conductive agent 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.

[0025] As a preferred technical solution of the present invention, 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, 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 the mass percentage of the negative electrode binder in the second layer.

[0026] As a preferred technical solution of the present invention, 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 the mass percentage of the negative electrode conductive agent in the second layer.

[0027] In a second aspect, the present invention provides a lithium-ion battery, comprising the electrode sheet described in the first aspect.

[0028] As a preferred technical solution of the present invention, 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.

[0029] Due to space limitations and to avoid redundancy, the present invention does not list all point values ​​within the above numerical range one by one, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0030] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0031] The present invention 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 problem 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 the binder in the active layer is reduced, thereby providing more space for the active material and fully improving the energy density. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0033] It should be clear to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0034] Example 1

[0035] This embodiment provides an electrode sheet:

[0036] 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;

[0037] Taking the mass of the positive electrode active layer as 100%, the positive electrode active layer includes 96.9% of positive electrode active material lithium manganese iron phosphate, 1.1% of positive electrode conductive agent (Super P and CNT with a mass ratio of 1:1), and 2% of positive electrode binder PVDF;

[0038] Taking the mass of the positive electrode second layer as 100%, the positive electrode second layer includes 97.7% of positive electrode active material lithium manganese iron phosphate, 1.1% of positive electrode conductor (SuperP and CNT with a mass ratio of 1:1), and 1.2% of positive electrode binder PVDF;

[0039] Taking the mass of the positive electrode first layer as 100%, the positive electrode first layer includes 96.1% of positive electrode active material lithium manganese iron phosphate, 1.1% of positive electrode conductor (SuperP and CNT with a mass ratio of 1:1), and 2.8% of positive electrode binder PVDF;

[0040] In the positive electrode active layer, the ratio of the mass percentage content of the positive electrode binder in the first positive electrode layer to the mass percentage content of the positive electrode binder in the second positive electrode layer is 2.33:1.

[0041] Example 2

[0042] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is changed, and the mass percentage ratio of the positive electrode binder in the first positive electrode layer and the second positive electrode layer is kept unchanged at 2.33:1, that is:

[0043] Based on 100% by mass of the positive electrode active layer, the positive electrode active layer includes 97.2% of positive electrode active material, 1.1% of positive electrode conductive agent, and 1.7% of positive electrode binder;

[0044] 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;

[0045] 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;

[0046] Except for the above, other conditions are exactly the same as those in Example 1.

[0047] Example 3

[0048] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is changed, and the mass percentage ratio of the positive electrode binder in the first positive electrode layer and the second positive electrode layer is kept unchanged at 2.33:1, that is:

[0049] 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;

[0050] 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;

[0051] 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;

[0052] Except for the above, other conditions are exactly the same as those in Example 1.

[0053] Example 4

[0054] This embodiment provides an electrode sheet, in which the total mass percentage of the positive electrode binder is changed, and the mass percentage ratio of the positive electrode binder in the first positive electrode layer and the second positive electrode layer is kept unchanged at 2.33:1, that is:

[0055] Based on 100% by mass of the positive electrode active layer, the positive electrode active layer includes 96.6% of positive electrode active material, 1.1% of positive electrode conductive agent, and 2.3% of positive electrode binder;

[0056] 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;

[0057] 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;

[0058] Except for the above, other conditions are exactly the same as those in Example 1.

[0059] Example 5

[0060] 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 and the second positive electrode layer is changed to 1.1:1, that is:

[0061] 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;

[0062] 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;

[0063] Except for the above, other conditions are exactly the same as those in Example 1.

[0064] Example 6

[0065] 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 and the second positive electrode layer is changed to 2.5:1, that is:

[0066] 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;

[0067] 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;

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

[0069] Example 7

[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 and the second positive electrode layer is changed to 2.8:1, that is:

[0071] 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;

[0072] 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;

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

[0074] Example 8

[0075] This embodiment provides an electrode sheet:

[0076] 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;

[0077] 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 SuperP, and 2.7% of negative electrode binder (1.5% of SBR and 1.2% of CMC);

[0078] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 97.96% of negative electrode active material graphite, 0.24% of negative electrode conductive agent SuperP, and 1.8% of negative electrode binder (0.6% of SBR and 1.2% of CMC);

[0079] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 95.44% of negative electrode active material graphite, 0.96% of negative electrode conductive agent SuperP, and 3.6% of negative electrode binder (2.4% of SBR and 1.2% of CMC);

[0080] 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; 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.

[0081] Example 9

[0082] 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 and the second negative electrode layer is kept constant at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer and the second negative electrode layer is kept constant 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 kept constant at 4:1, that is:

[0083] Taking the mass of the negative electrode active layer as 100%, the negative electrode active layer includes 97.3% of negative electrode active material graphite, 0.6% of negative electrode conductive agent SuperP, and 2.1% of negative electrode binder (1.17% of SBR and 0.93% of CMC);

[0084] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 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);

[0085] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 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);

[0086] Except for the above, other conditions are exactly the same as those in Example 8.

[0087] Example 10

[0088] 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 and the second negative electrode layer is kept constant at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer and the second negative electrode layer is kept constant 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 kept constant at 4:1, that is:

[0089] Taking the mass of the negative electrode active layer as 100%, the negative electrode active layer includes 96.1% of negative electrode active material graphite, 0.6% of negative electrode conductive agent SuperP, and 3.3% of negative electrode binder (1.83% of SBR and 1.47% of CMC);

[0090] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 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);

[0091] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 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);

[0092] Except for the above, other conditions are exactly the same as those in Example 8.

[0093] Embodiment 11

[0094] This embodiment 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 of the first negative electrode layer and the second negative electrode layer is kept unchanged at 2:1, the mass percentage ratio of the SBR of the first negative electrode layer and the second negative electrode layer is changed to 0.88:1, and the mass percentage ratio of the negative electrode conductive agent of the first negative electrode layer and the second negative electrode layer is kept unchanged at 4:1, that is:

[0095] 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;

[0096] 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;

[0097] Except for the above, other conditions are exactly the same as those in Example 8.

[0098] Example 12

[0099] This embodiment 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 of the first negative electrode layer and the second negative electrode layer is kept unchanged at 2:1, the mass percentage ratio of the SBR of the first negative electrode layer and the second negative electrode layer is changed to 1.14:1, and the mass percentage ratio of the negative electrode conductive agent of the first negative electrode layer and the second negative electrode layer is kept unchanged at 4:1, that is:

[0100] 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;

[0101] 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;

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

[0103] Example 13

[0104] This embodiment 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 of the first negative electrode layer and the second negative electrode layer is kept unchanged at 2:1, the mass percentage ratio of the SBR of the first negative electrode layer and the second negative electrode layer is changed to 2:1, and the mass percentage ratio of the negative electrode conductive agent of the first negative electrode layer and the second negative electrode layer is kept unchanged 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% of SBR and 0.8% of CMC;

[0106] Based on 100% of the mass of the negative electrode first layer, 3.6% of the negative electrode binder in the negative electrode first layer is composed of 2% of SBR and 1.6% of CMC;

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

[0108] Embodiment 14

[0109] This embodiment 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 kept unchanged at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer and 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 and the second negative electrode layer is kept unchanged 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 0.5% of SBR and 1.3% 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 2.5% of SBR and 1.1% of CMC;

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

[0113] Embodiment 15

[0114] This embodiment 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 1.1:1, but the mass percentage ratio of the SBR in the first negative electrode layer and the second negative electrode layer is kept unchanged at 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 kept unchanged at 4:1, that is:

[0115] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 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);

[0116] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 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);

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

[0118] Example 16

[0119] This embodiment 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 4:1, but the mass percentage ratio of the SBR in the first negative electrode layer and the second negative electrode layer is kept unchanged at 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 kept unchanged at 4:1, that is:

[0120] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 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);

[0121] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 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);

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

[0123] Embodiment 17

[0124] This embodiment 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 5:1, but the mass percentage ratio of the SBR in the first negative electrode layer and the second negative electrode layer is kept unchanged at 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 kept unchanged at 4:1, that is:

[0125] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 98.86% of negative electrode active material graphite, 0.24% of negative electrode conductive agent SuperP, and 0.9% of negative electrode binder (0.6% of SBR and 0.3% of CMC);

[0126] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 94.54% of negative electrode active material graphite, 0.96% of negative electrode conductive agent SuperP, and 4.5% of negative electrode binder (2.4% of SBR and 2.1% of CMC);

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

[0128] Embodiment 18

[0129] This embodiment 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 kept unchanged at 2:1, the mass percentage ratio of the SBR in the first negative electrode layer and the second negative electrode layer is kept unchanged at 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 1:1, that is:

[0130] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 97.6% of negative electrode active material graphite, 0.6% of negative electrode conductive agent SuperP, and 1.8% of negative electrode binder (0.6% of SBR and 1.2% of CMC);

[0131] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 95.8% of negative electrode active material graphite, 0.6% of negative electrode conductive agent SuperP, and 3.6% of negative electrode binder (2.4% of SBR and 1.2% of CMC);

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

[0133] Comparative Example 1

[0134] This comparative example provides an electrode sheet, the positive electrode active layer of the electrode sheet is not layered, that is:

[0135] 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. Taking the mass of the positive electrode active layer as 100%, the positive electrode active layer includes 96.9% of positive electrode active material lithium manganese iron phosphate, 1.1% of positive electrode conductive agent (SuperP and CNT with a mass ratio of 1:1), and 2% of positive electrode binder PVDF.

[0136] Comparative Example 2

[0137] This comparative example provides an electrode sheet, the positive electrode active layer of the electrode sheet is not layered, that is:

[0138] 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 SuperP, and 2.7% of negative electrode binder (1.5% SBR and 1.2% CMC).

[0139] Comparative Example 3

[0140] 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:

[0141] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 97.06% of negative electrode active material graphite, 0.24% of negative electrode conductive agent SuperP, and 2.7% of negative electrode binder (1.5% of SBR and 1.2% of CMC);

[0142] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 96.34% of negative electrode active material graphite, 0.96% of negative electrode conductive agent SuperP, and 2.7% of negative electrode binder (1.5% of SBR and 1.2% of CMC);

[0143] Except for the above, other conditions are exactly the same as those in Example 8.

[0144] Comparative Example 4

[0145] 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:

[0146] Taking the mass of the negative electrode second layer as 100%, the negative electrode second layer includes 97.06% of negative electrode active material graphite, 0.24% of negative electrode conductive agent SuperP, and 2.7% of negative electrode binder (0.6% of SBR and 2.1% of CMC);

[0147] Taking the mass of the negative electrode first layer as 100%, the negative electrode first layer includes 96.34% of negative electrode active material graphite, 0.96% of negative electrode conductive agent SuperP, and 2.7% of negative electrode binder (2.4% of SBR and 0.3% of CMC);

[0148] Except for the above, other conditions are exactly the same as those in Example 8.

[0149] Characterization and Testing:

[0150] Ⅰ. Peel force test:

[0151] 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.

[0152] The coating peeling force and cold pressing peeling force of the electrode sheets obtained in Examples 1-18 and Comparative Examples 1-4 during the manufacturing process were tested, and the results are listed in Table 1;

[0153] Table 1

[0154]

[0155]

[0156] The results show that the stripping force of the electrode is proportional to the binder content at the contact point of the current collector. The higher the binder content of the first layer, the higher the coating stripping force, and the higher the relative cold pressing stripping force. The negative electrode CMC content has little to do with the stripping force, and the stripping force depends on the SBR content.

[0157] Ⅱ. Select the electrode sheet provided by any one of Examples 1-7 and Comparative Example 1 as the positive electrode, and select the electrode sheet provided by 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, and after lamination, drying, liquid injection (the electrolyte is 1 mol / L LiPF6 ethyl carbonate (EC) + dimethyl carbonate solution (DMC), the mass percentage of additives: 2% fluoroethylene carbonate (FEC)), packaging, formation and constant volume, a lithium iron manganese phosphate battery is obtained.

[0158] 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 charging, 1C constant current discharging). The results are recorded in Table 2.

[0159] Table 2

[0160]

[0161]

[0162] From the assembly of the battery cell by positive electrode examples 2-4 and negative electrode example 8 in Table 2, it can be seen that the increase in the binder content of the positive electrode solution did not reduce the internal resistance of the battery cell, but reduced the cycle attenuation. The increase in the total binder content makes the positive electrode active material and the current collector more closely combined during the battery cell cycle, and the material conduction does not weaken as the number of cycles increases. Positive electrode examples 5-7 indicate that: because the negative electrode electrons are concentrated at the contact point between the first layer and the current collector during charging and discharging, the higher the SBR content of the first layer, the more significant the effect.

[0163] The negative electrode example shows that as the conductive agent content of the first layer increases, the internal resistance of the battery cell decreases. Changes in the binder do not affect the internal resistance value. The negative electrode cycle performance is the result of the combined action of the conductive agent and the binder. The lower the internal resistance value, that is, the higher the conductive agent content of the first layer, the better the cycle performance; the higher the binder content of the first layer, the better the cycle performance. Compared with Comparative Examples 1 and 2, the internal resistance and cycle performance of the battery cell in the component layered scheme are significantly better than those of the non-layered uniform electrode.

[0164] The present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0165] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0166] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0167] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An electrode sheet, characterized in that: It includes a current collector and an active layer arranged on the current collector, the active layer 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 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, characterized in that: When the electrode sheet is a positive electrode, the active layer includes a positive electrode active material, a positive electrode conductive agent and a positive electrode binder; Preferably, the positive electrode active material comprises lithium manganese iron phosphate; Preferably, the positive electrode binder comprises PVDF.

3. The electrode sheet according to claim 2, characterized in that: Taking the mass of the active layer of the positive electrode as 100%, the total mass percentage of the positive electrode binder is 0.1% to 2%; Preferably, based on the mass of the positive electrode active layer being 100%, the total mass percentage of the positive electrode active material is 96% to 98%, the total mass percentage of the positive electrode binder is 0.5% to 1.8%, and the total mass percentage of the positive electrode conductor is 0.2% to 3.5%.

4. The electrode sheet according to claim 2 or 3, characterized in that: 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.

5. The electrode sheet according to any one of claims 1 to 4, characterized in that: 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; Preferably, the negative electrode binder comprises SBR.

6. The electrode sheet according to claim 5, characterized in that: Taking 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%; Preferably, based on the mass of the negative electrode active layer being 100%, the total mass percentage of the negative electrode active material is 95% to 99%, the total mass percentage of the negative electrode binder is 0.8% to 3%, and the total mass percentage of the negative electrode conductor is 0.2% to 2%.

7. The electrode sheet according to claim 5 or 6, characterized in that: 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.

8. The electrode sheet according to any one of claims 5 to 7, characterized in that: 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.

9. A lithium ion battery, characterized in that: The electrode sheet comprises the electrode sheet according to any one of claims 1 to 8.

10. The lithium ion battery according to claim 9, characterized in that: The lithium-ion battery comprises 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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