Positive pole piece and preparation method thereof, battery and power utilization device

Abstract

The invention discloses a positive pole piece and a preparation method thereof, a battery and an electric device. The positive pole piece comprises a positive current collector and a positive active material layer, the positive active material layer is arranged on at least one side of the positive current collector, and lithium powder is dispersed on one side, far away from the positive current collector, of the positive active material layer. The lithium powder dispersed on the positive pole piece can effectively capture moisture in the positive pole active material, so that the moisture is effectively prevented from reacting with the electrolyte lithium salt to generate HF, and the gas production of the battery is remarkably reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular, relates to a positive electrode plate and a preparation method thereof, a battery, and an electrical device. Background Art

[0002] In recent years, the world has focused on developing sustainable energy in order to effectively respond to the challenges of energy crisis and environmental pollution. Among them, lithium-ion batteries have been vigorously developed because they can achieve efficient, clean and sustainable energy storage, and new energy vehicles have also attracted global attention. Lithium-ion power batteries are not only the best choice for new energy vehicles at this stage, but also the most widely used type of battery in new energy vehicles at this stage. Therefore, the improvement of the overall electrical performance of lithium-ion batteries (electrical performance under different environments) and the reduction of their costs are the main goals of competition among manufacturers in various countries. For various power battery systems, gas production is one of the important factors affecting the safety and life of the battery cell.

[0003] The existing method of reducing the gas production of battery cells is mainly to narrow the operating voltage window of the system, but this operation will cause the energy density of the battery cell to decrease. Or avoid using certain additives in the battery cell, but such additives can repair the negative electrode SEI film (solid electrolyte interface) during the battery cell cycle and storage process, which may reduce the service life of the battery cell. Therefore, it is urgent to find an effective means to solve the gas production problem of the battery cell. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one object of the present invention is to provide a positive electrode plate and a preparation method thereof, a battery, and an electrical device. The lithium powder dispersed on the positive electrode plate can effectively capture moisture in the positive electrode active material, effectively avoiding the reaction of moisture with electrolyte lithium salt to generate HF, and significantly reducing battery gas production.

[0005] In one aspect of the present invention, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, the positive electrode sheet comprises:

[0006] Positive electrode current collector;

[0007] A positive electrode active material layer is provided on at least one side of the positive electrode current collector, and lithium powder is dispersed on a side of the positive electrode active material layer away from the positive electrode current collector.

[0008] The positive electrode sheet according to an embodiment of the present invention includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer is arranged on at least one side of the positive electrode current collector, and lithium powder is dispersed on the side of the positive electrode active material layer away from the positive electrode current collector. The lithium powder can effectively capture the moisture in the positive electrode active material, effectively avoid the reaction of moisture with the electrolyte lithium salt to generate HF, and significantly reduce the gas production of the battery. As a result, the battery containing the positive electrode sheet has low gas production and thus has excellent electrical performance.

[0009] In addition, the positive electrode sheet according to the above embodiment of the present invention may also have the following technical features:

[0010] In some embodiments of the present invention, the positive electrode active material layer includes a positive electrode active material, and the amount of the lithium powder is 0.005wt% to 5wt% based on the total mass of the positive electrode active material, thereby reducing the amount of water dissolved from the positive electrode active material layer and significantly reducing the gas generation of the battery.

[0011] In some embodiments of the present invention, the particle size D of the lithium powder is 50 This can reduce the amount of water eluted from the positive electrode active material layer and significantly reduce battery gas generation.

[0012] In some embodiments of the present invention, the lithium powder includes at least one of metallic lithium powder and passivated lithium powder. Thus, the amount of water dissolved from the positive electrode active material layer can be reduced, and the gas generation of the battery can be significantly reduced.

[0013] In some embodiments of the present invention, the passivated lithium powder includes metal lithium powder and a coating layer coated on the surface of the metal lithium powder, and the coating layer includes at least one of lithium fluoride, lithium carbonate, lithium nitride, metal cobalt, and metal silver. In this way, the amount of water dissolution from the positive electrode active material layer can be reduced, and the gas generation of the battery can be significantly reduced.

[0014] In some embodiments of the present invention, the mass proportion of the coating layer is 2% to 30% based on the total mass of the passivated lithium powder, thereby reducing the amount of water dissolved from the positive electrode active material layer and significantly reducing battery gas generation.

[0015] In some embodiments of the present invention, the surface density of the positive electrode sheet is 300g / m 2 ~500g / m 2 ; and / or, the compaction density of the positive electrode sheet is 2.20g / cm 3 ~3.6g / cm 3 .

[0016] In a second aspect of the present invention, the present invention provides a method for preparing the above-mentioned positive electrode sheet. According to an embodiment of the present invention, the method comprises:

[0017] (1) applying a positive electrode slurry to at least one side of a positive electrode current collector to form a positive electrode active material layer on the positive electrode current collector;

[0018] (2) Lithium powder is applied to the positive electrode active material layer on a side away from the positive electrode current collector to obtain a positive electrode sheet.

[0019] Therefore, the method can be used to disperse lithium powder on the side of the positive electrode active material layer away from the positive electrode current collector, that is, to prepare a positive electrode sheet with lithium powder dispersed on the positive electrode active material layer. The lithium powder can effectively capture the moisture in the positive electrode active material, effectively avoiding the reaction of moisture with the electrolyte lithium salt to generate HF, and significantly reducing gas production. Therefore, the battery containing the positive electrode sheet obtained by this method has low gas production and thus has excellent electrical performance.

[0020] In addition, the method for preparing a positive electrode sheet according to the above embodiment of the present invention may also have the following technical features:

[0021] In some embodiments of the present invention, before applying lithium powder to the side of the positive electrode active material layer away from the positive electrode current collector, the positive electrode active material layer is pre-heated.

[0022] In some embodiments of the present invention, the lithium powder is applied to the side of the positive electrode active material layer away from the positive electrode current collector by rolling, thereby dispersing the lithium powder on the side of the positive electrode active material layer away from the positive electrode current collector.

[0023] In a third aspect of the present invention, a battery is provided. According to an embodiment of the present invention, the battery comprises the above-mentioned positive electrode sheet, and / or the positive electrode sheet prepared by the above-mentioned method. As a result, the battery cell system has a low gas generation level, thereby having excellent electrical performance and a long service life.

[0024] In some embodiments of the present invention, the battery further comprises: an electrolyte, wherein the electrolyte has an injection coefficient of 2.0 g / Ah to 4.5 g / Ah.

[0025] In a fourth aspect of the present invention, the present invention provides an electric device. According to an embodiment of the present invention, the electric device comprises the above-mentioned battery. Thus, the electric device has excellent energy storage performance and a long service life.

[0026] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0028] Figure 1 Schematic diagram of the positive electrode structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0030] The technical solution of the present invention is completed by the inventor based on the following findings: gas production is one of the important factors affecting the safety and life of the battery cell. Under the premise of not affecting the energy density and service life of the battery cell, how to reduce the gas production of the battery cell is an important means to improve the electrical performance of the battery. Part of the reason for the gas production of the battery cell is that the water in the battery cell and the lithium salt (lithium hexafluorophosphate) are hydrolyzed to form HF. This is mainly due to the presence of water inside the battery cell that cannot be baked out, especially the water in the positive active material is more difficult to bake out. Therefore, after the electrolyte is injected, the water in the positive active material that has not been baked out will dissolve, and then react with the lithium salt to form HF. First, HF will react with alkaline substances in the battery cell such as the SEI membrane, destroy the internal structure of the battery cell, and then degrade the material performance, so that the degraded material reacts with the solvent, etc., and accelerates the gas production of the battery cell; secondly, HF directly reacts with the Li-type substances in the battery cell to produce gas. Therefore, if the water in the battery cell can be controlled and reduced, especially the water in the positive active material can be controlled to dissolve into the electrolyte to avoid the reaction of water with the electrolyte to form HF, it is very important to solve the gas production of the battery cell.

[0031] In view of this, in one aspect of the present invention, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, referring to Figure 1 The positive electrode sheet includes: a positive electrode current collector 100 and a positive electrode active material layer 200 , wherein the positive electrode active material layer 200 is disposed on at least one side of the positive electrode current collector 100 , and lithium powder 300 is dispersed on the side of the positive electrode active material layer 200 away from the positive electrode current collector 100 .

[0032] The inventors found that for the positive electrode sheets that are most difficult to bake out moisture, by dispersing lithium powder 300 on the side of the positive active material layer 200 of the positive electrode sheet away from the positive current collector 100, the lithium powder 300 has a strong ability to capture moisture. Therefore, the lithium powder 300 can capture and absorb the moisture that cannot be removed by baking in the positive active material layer 200, thereby effectively avoiding the dissolution of moisture from the positive active material layer 200 and reacting with lithium salts, and greatly reducing the gas production level of the battery system.

[0033] It should be noted that the positive electrode current collector 100 is a conventional component in the art, and those skilled in the art may select it according to actual conditions. For example, the positive electrode current collector 100 is made of aluminum foil, composite aluminum foil or carbon-coated aluminum foil.

[0034] According to an embodiment of the present invention, the positive electrode active material layer 200 further includes a positive electrode active material. Based on the total mass of the positive electrode active material, the amount of lithium powder 300 is 0.005wt% to 5wt%, for example, 0.005wt%, 0.01wt%, 0.05wt%, 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, etc. Thus, by adding the above amount of lithium powder to the positive electrode active material layer 200, the water dissolved from the positive electrode active material can be effectively captured, and the water can be effectively prevented from dissolving from the positive electrode active material layer 200 and reacting with the lithium salt, thereby greatly reducing the gas generation level of the battery system. The lithium powder 300 can be randomly dispersed or evenly dispersed on the side of the positive electrode active material layer 200 away from the positive electrode current collector 100, and the present invention does not limit it. When the lithium powder content is within the above range, the moisture content in the positive electrode active material layer can be better absorbed, and battery safety problems will not be caused by excessive lithium powder.

[0035] It should be noted that the positive electrode active material is a conventional material in the field, and those skilled in the art can select it according to actual conditions. For example, the positive electrode active material includes lithium iron phosphate, lithium nickel oxide, lithium manganese oxide, lithium manganese phosphate, lithium manganese phosphate, lithium manganese iron phosphate, etc.

[0036] According to an embodiment of the present invention, the D of the lithium powder 300 50 5 μm to 40 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, etc. Therefore, this application adopts D 50 The lithium powder 300 with a diameter of 5 μm to 40 μm can effectively capture the water dissolved from the positive electrode active material, effectively prevent the water from dissolving from the positive electrode active material layer 200 and reacting with the lithium salt, and greatly reduce the gas generation level of the battery system. 50 It refers to the particle size corresponding to when the cumulative volume distribution percentage reaches 50%.

[0037] According to an embodiment of the present invention, the lithium powder 300 includes at least one of metallic lithium powder and passivated lithium powder. Preferably, the passivated lithium powder includes metallic lithium powder and a coating layer coated on the surface of the metallic lithium powder, and the coating layer includes at least one of lithium fluoride, lithium carbonate, lithium nitride, metallic cobalt, and metallic silver. Because the passivated lithium powder is coated with a coating layer on the surface of the metallic lithium powder, for example, when the coating layer is lithium fluoride, lithium carbonate, or lithium nitride, the coating layer can be dissolved in the electrolyte after injection. When the coating layer is dissolved in the electrolyte, the lithium powder is exposed, so that the water leached from the positive electrode material can be captured. Through the dissolution process of the coating layer, the reaction degree of the passivated lithium powder and the water can be alleviated, thereby improving the absorption and capture ability of the passivated lithium powder for the water in the positive electrode material. For another example, if the coating layer is metal cobalt or metal silver, since the coating layer cannot completely cover the surface of the metal lithium powder, part of the metal lithium powder surface will inevitably be exposed. Therefore, the presence of the coating layer reduces the contact area between the metal lithium powder and water, and alleviates the degree of reaction between the passivated lithium powder and water, thereby improving the passivated lithium powder's ability to absorb and capture water in the positive electrode material. Specifically, based on the total mass of the passivated lithium powder, the mass of the coating layer accounts for 2%-30%, thereby effectively controlling the degree of reaction between the passivated lithium powder and water and improving the ability to adsorb water in the positive electrode material.

[0038] According to an embodiment of the present invention, the positive electrode active material layer 200 may further include a conductive agent, for example, the conductive agent may include one or more of conductive carbon black (SP), carbon nanotubes (CNT), graphene, and conductive graphite. Thus, by adding a conductive agent to the positive electrode active material layer, the ionic conductivity of the positive electrode sheet can be improved, thereby improving the power performance of the battery.

[0039] According to an embodiment of the present invention, the positive active material layer 200 further includes a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and a cellulose-based polymer.

[0040] According to an embodiment of the present invention, the surface density of the positive electrode sheet is 300g / m 2 ~500g / m 2 ; and / or, the compaction density of the positive electrode sheet is 2.20g / cm 3 ~3.6g / cm 3 For example, the surface density is 300g / m 2 , 320g / m 2 , 350g / m 2 , 380g / m 2 , 400g / m 2 , 420g / m 2 , 450g / m 2 , 500g / m 2etc.; compacted density is 2.20g / cm 3 , 2.50g / cm 3 , 2.80g / cm 3 、3.00g / cm 3 、3.20g / cm 3 、3.40g / cm 3 、3.60g / cm 3 wait.

[0041] The lithium powder dispersed on the positive electrode plate can effectively capture the moisture in the positive electrode active material, effectively avoiding the reaction between the moisture and the electrolyte lithium salt to generate HF, and significantly reducing the gas production of the battery cell. As a result, the battery containing the positive electrode plate has low gas production, thus having excellent electrical performance and a long service life.

[0042] In a second aspect of the present invention, the present invention provides a method for preparing the above-mentioned positive electrode sheet. According to an embodiment of the present invention, the method comprises:

[0043] S100: Applying the positive electrode slurry to at least one side of the positive electrode current collector

[0044] In this step, the positive electrode slurry is applied to at least one side of the positive electrode current collector, thereby forming a positive electrode active material layer on the positive electrode current collector. It should be noted that the positive electrode slurry is a commonly used material in the art, and the positive electrode slurry is usually a mixture of a positive electrode active material, a binder, a conductive agent and a solvent. Those skilled in the art can select the type and content of the positive electrode active material, the binder and the conductive agent according to actual conditions, and there is no special limitation here. For example, the binder includes polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), cellulose-based polymers, etc.; the conductive agent includes one or more of conductive carbon black (SP), carbon nanotubes (CNT), graphene, and conductive graphite; the amount of solvent used can meet the fluidity and uniformity of the slurry coating, and the solvent can include one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), water and alcohols, preferably N-methylpyrrolidone (NMP). At the same time, the method of applying the positive electrode slurry to the positive electrode current collector is also a conventional method in the art, such as spraying, coating, etc.

[0045] S200: Apply lithium powder to the positive electrode active material layer on the side away from the positive electrode current collector

[0046] In this step, lithium powder is applied to the side of the positive electrode active material layer away from the positive electrode current collector, thereby obtaining a positive electrode sheet.

[0047] According to an embodiment of the present invention, after the positive electrode slurry in S100 is coated on the current collector, lithium powder is evenly applied to the surface of the positive electrode slurry on the side away from the positive electrode current collector after coating, and then dried together, so that the lithium powder is evenly dispersed on the surface of the positive electrode active material layer, thereby obtaining a positive electrode sheet containing lithium powder.

[0048] According to an embodiment of the present invention, before applying lithium powder to the side of the positive electrode active material layer away from the positive electrode current collector, the positive electrode active material layer is preheated, that is, after the positive electrode slurry is coated on the current collector, a drying treatment is performed to remove the solvent in the positive electrode slurry, thereby forming a dried positive electrode active material layer on the current collector, and then the lithium powder is applied to the side of the dried positive electrode active material layer away from the positive electrode current collector by roller pressing, thereby obtaining a positive electrode sheet containing lithium powder.

[0049] Therefore, the method can be used to disperse lithium powder on the side of the positive electrode active material layer away from the positive electrode current collector, that is, to prepare a positive electrode sheet with lithium powder dispersed on the positive electrode active material layer. The lithium powder can effectively capture the moisture in the positive electrode active material, effectively avoiding the reaction of moisture with the electrolyte lithium salt to generate HF, and significantly reducing the gas production of the battery cell. Therefore, the battery gas production of the positive electrode sheet obtained by this method is low, so it has excellent electrical performance and a long service life.

[0050] In a third aspect of the present invention, a battery is provided. According to an embodiment of the present invention, the battery comprises the positive electrode sheet and / or the positive electrode sheet prepared by the method. As a result, the battery cell system has a low gas generation level, thereby having excellent electrical performance and a long service life.

[0051] Furthermore, the battery also includes an electrolyte, and the electrolyte injection coefficient is 2.0g / Ah to 4.5g / Ah, for example, the injection coefficient is 2.0g / Ah, 2.5g / Ah, 3.0g / Ah, 3.5g / Ah, 4.0g / Ah, 4.5g / Ah, etc.

[0052] According to an embodiment of the present invention, the electrolytic solution includes an electrolyte salt and a solvent.

[0053] As an example, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0054] As an example, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, and fluoroethylene carbonate.

[0055] It can be understood by those skilled in the art that the battery also includes a negative electrode sheet and a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet and the separator are conventional battery components in the field. Those skilled in the art can select the negative electrode sheet and the separator as well as the preparation process of the negative electrode sheet according to actual conditions.

[0056] For example, the negative electrode plate includes a negative electrode current collector and a negative electrode active material. The negative electrode current collector can be made of copper foil, and the negative electrode active material includes a negative electrode material, a conductive agent, and a binder.

[0057] As an example, the negative electrode material may be graphite, such as artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like.

[0058] As an example, the adhesive includes polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), cellulose-based polymers, etc.; the conductive agent includes one or more of conductive carbon black (SP), carbon nanotubes (CNT), graphene, conductive graphite, etc.

[0059] As an example, the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0060] It should be noted that the features and advantages described above for the positive electrode plate and its preparation method are also applicable to the battery and will not be repeated here.

[0061] In a fourth aspect of the present invention, the present invention provides an electric device. According to an embodiment of the present invention, the electric device includes the above-mentioned battery. As a result, the electric device has excellent energy storage performance and a long service life. For example, the electric device may include but is not limited to a pure electric vehicle, a hybrid electric vehicle, etc.

[0062] It should be noted that the features and advantages described above for the battery are also applicable to the electrical device and will not be described in detail here.

[0063] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0064] Example 1

[0065] (1) Preparation of positive electrode sheet

[0066] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.002% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.002%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0067] (2) Preparation of negative electrode sheet

[0068] Graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber and water are mixed and stirred in a mass ratio of 100:1.5:3:130 to obtain a uniform negative electrode slurry, and the negative electrode slurry is evenly coated on the upper and lower surfaces of a conductive copper foil with a thickness of 8 μm, dried and rolled at 110° C., and finally a negative electrode sheet is obtained by slitting and die-cutting;

[0069] (3) Preparation of batteries

[0070] The positive electrode sheet, negative electrode sheet and polypropylene separator are stacked in a Z-shaped stacking manner to assemble a lithium-ion battery core, and then hot-pressed into a square soft-pack battery cell with a length of 800 mm, a width of 16 mm and a height of 90 mm. The battery is obtained through processes such as liquid injection, aging, formation and aging.

[0071] (4) Moisture content test of positive electrode

[0072] In a -40°C dew point environment, the electrode core is baked according to the normal baking process. After baking, the positive electrode sheet is taken out and sealed in a -40°C environment, and then sent to a Karl Fischer tester to test the moisture content at 160°C in ppm. The initial moisture content of the positive electrode sheet is 176.2ppm.

[0073] Example 2

[0074] The main differences between Example 2 and Example 1 are as follows:

[0075] (1) Preparation of positive electrode sheet

[0076] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.005% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.005%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0077] (4) The initial moisture content of the positive electrode sheet is 170.3 ppm.

[0078] Example 3

[0079] The difference between Example 3 and Example 1 is as follows:

[0080] (1) Preparation of positive electrode sheet

[0081] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.05% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.05%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0082] (4) The initial moisture content of the positive electrode sheet was 168.9 ppm.

[0083] Example 4

[0084] The difference between Example 4 and Example 1 is as follows:

[0085] (1) Preparation of positive electrode sheet

[0086] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.1% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.1%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0087] (4) The initial moisture content of the positive electrode sheet is 182.3 ppm.

[0088] Example 5

[0089] The difference between Example 5 and Example 1 is as follows:

[0090] (1) Preparation of positive electrode sheet

[0091] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.5% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.5%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0092] (4) The initial moisture content of the positive electrode sheet is 177.5 ppm.

[0093] Example 6

[0094] The difference between Example 6 and Example 1 is as follows:

[0095] (1) Preparation of positive electrode sheet

[0096] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 2% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 2%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0097] (4) The initial moisture content of the positive electrode sheet is 167.2 ppm.

[0098] Example 7

[0099] The difference between Example 7 and Example 1 is as follows:

[0100] (1) Preparation of positive electrode sheet

[0101] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 3% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 1.5%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0102] (4) The initial moisture content of the positive electrode sheet is 167.2 ppm.

[0103] Example 8

[0104] The difference between Example 8 and Example 1 is as follows:

[0105] (1) Preparation of positive electrode sheet

[0106] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 4% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 1.5%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0107] (4) The initial moisture content of the positive electrode sheet was 183.1 ppm.

[0108] Example 9

[0109] The differences between Example 9 and Example 1 are as follows:

[0110] (1) Preparation of positive electrode sheet

[0111] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 5% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 1.5%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0112] (4) The initial moisture content of the positive electrode sheet was 183.7 ppm.

[0113] Example 10

[0114] The difference between Example 10 and Example 1 is as follows:

[0115] (1) Preparation of positive electrode sheet

[0116] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 6% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 1.5%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0117] (4) The initial moisture content of the positive electrode sheet is 176.4 ppm.

[0118] Embodiment 11

[0119] The differences between Example 11 and Example 1 are as follows:

[0120] (1) Preparation of positive electrode sheet

[0121] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.1% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.1%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0122] (4) The initial moisture content of the positive electrode sheet is 576 ppm.

[0123] Example 12

[0124] The differences between Example 12 and Example 1 are as follows:

[0125] (1) Preparation of positive electrode sheet

[0126] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.1% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.1%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0127] (4) The initial moisture content of the positive electrode sheet is 1104 ppm.

[0128] Embodiment 13

[0129] The differences between Example 13 and Example 1 are as follows:

[0130] (1) Preparation of positive electrode sheet

[0131] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 2% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 2%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0132] (4) The initial moisture content of the positive electrode sheet is 1131 ppm.

[0133] Embodiment 14

[0134] The difference between Example 14 and Example 1 is as follows:

[0135] (1) Preparation of positive electrode sheet

[0136] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.1% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.1%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0137] (4) The initial moisture content of the positive electrode sheet is 182.3 ppm.

[0138] Embodiment 15

[0139] The difference between Example 15 and Example 1 is as follows:

[0140] (1) Preparation of positive electrode sheet

[0141] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the passivation lithium powder (the coating layer of the passivation lithium powder is lithium fluoride, and the mass proportion of the coating layer is 15%) is evenly applied to the surface of the above-mentioned baked positive electrode material for roll pressing, thereby obtaining a positive electrode sheet containing the passivation lithium powder, wherein the addition amount of the passivation lithium powder is 0.1% of the mass of the positive electrode active material, and the D of the passivation lithium powder is 0.1%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0142] (4) The initial moisture content of the positive electrode sheet is 176.5 ppm.

[0143] Example 16

[0144] The main differences between Example 16 and Example 1 are as follows:

[0145] (1) Preparation of positive electrode sheet

[0146] The positive electrode active material (lithium iron phosphate-LFP), the conductive agent (CNT and SP), the binder (PVDF) and the solvent (NMP) are configured into a positive electrode slurry in a ratio of LFP:CNT:SP:PVDF:NMP=100:12:0.3:2.5:55 by mass, and the positive electrode slurry is evenly coated on the upper and lower surfaces of a 15 μm thick conductive aluminum foil, and then baked to obtain a positive electrode sheet, and finally the metal lithium powder is evenly applied to the surface of the baked positive electrode material for roll pressing to obtain a positive electrode sheet containing metal lithium powder, wherein the addition amount of the metal lithium powder is 0.005% of the mass of the positive electrode active material, and the D of the metal lithium powder is 0.005%. 50 The surface density of the positive electrode sheet is 400g / m 2 , compacted density is 2.6g / cm 3 .

[0147] (4) The initial moisture content of the positive electrode sheet is 177.3 ppm.

[0148] Comparative Example 1

[0149] The main difference between Comparative Example 1 and Example 1 is that no lithium powder is added in Comparative Example 1, and the initial moisture content of the positive electrode sheet obtained in Comparative Example 1 is 171.7 ppm.

[0150] Comparative Example 2

[0151] The main difference between Comparative Example 2 and Example 1 is that no lithium powder is added in Comparative Example 2, and the initial moisture content of the positive electrode sheet obtained in Comparative Example 2 is 541 ppm.

[0152] Comparative Example 3

[0153] The main difference between Comparative Example 3 and Example 1 is that no lithium powder is added in Comparative Example 3, and the initial moisture content of the positive electrode plate obtained in Comparative Example 3 is 1098 ppm.

[0154] The gas generation level of the battery cells obtained in Examples 1-16 and Comparative Examples 1-3, as well as the capacity and cycle performance of the battery and whether lithium is deposited on the negative electrode plate are tested. The specific test method is as follows:

[0155] (1) Capacity test: At 25°C, fully charge the battery to 3.8V at 0.33C constant current and constant voltage, then discharge it to 2.0V at 0.33C constant current after standing for 3 times. The third discharge capacity is recorded as C0. The ratio of C0 to the mass of active material is the gram capacity Q of the material.

[0156] (2) Battery cycle performance test at 45°C: At 25°C, charge and discharge three times at 0.33C, with a voltage range of 2.0-3.8V, and calibrate the third discharge capacity as the battery capacity C0; after calibrating the capacity, charge to 3.8V at 1C0 constant current and constant voltage at 45°C, with a cut-off current of 0.05C0, then let stand for 30 minutes, discharge to 2.0V at 1C0 constant current, then let stand for 30 minutes; cycle the above steps 1000 times, the discharge capacity of the 1000th cycle is C1, and the cycle capacity retention rate of the battery cell = C1 / C0*100%;

[0157] (3) Gas production test: At 25°C, charge to 3.8V with 0.33C0 and leave for 30min, then discharge to 2.0V with 0.33C0 and leave for 30min, then fix the lower ends of the two copper wires on both sides of the battery cell, and connect the upper ends of the copper wires to the electronic balance hook, then immerse the battery cell completely in silicone oil. After all the bubbles in the silicone oil have escaped and the readings are stable, m1 is obtained in g. After (2) cycles, m2 is obtained in g using the above method, V = (m1-m2) / ρ 硅油 The gas production during the cycle is obtained in ml; A=V / C0 is converted into ml / Ah.

[0158] (4) Whether the negative electrode plate has lithium deposition: After the capacity test in (1), the battery cell is disassembled in the glove box to remove the negative electrode plate, the negative electrode plate is sealed with a glass slide and sealant, and the negative electrode plate is observed through the glass slide using a confocal microscope.

[0159] The test results of the gas generation levels of the batteries of Examples 1-16 and Comparative Examples 1-3 are shown in Table 1.

[0160] Table 1

[0161]

[0162]

[0163] As can be seen from Table 1, by comparing Examples 1-10 with Comparative Example 1, under the same initial moisture content of the positive electrode sheet, as the content of passivation lithium powder in the positive electrode sheet increases, its 45°C cycle gas production will decrease as the amount of passivation lithium powder added increases. Compared with Comparative Example 1 without adding lithium powder, the 45°C cycle gas production of Examples 2-10 is significantly reduced, indicating that the positive electrode sheet of the present application can significantly reduce the gas production level of the battery.

[0164] By comparing Examples 4, 11, 12 with Comparative Examples 2 and 3, it can be seen that when the initial moisture content of the positive electrode plate increases, its 45°C cycle gas production will increase, but compared with Examples 4, 11, 12 and Comparative Examples 2 and 3 without adding lithium powder, the 45°C cycle gas production is still significantly reduced; by comparing Examples 12, 13 with Comparative Example 3, it can be seen that under the same initial moisture content, increasing the content of passivation lithium powder will significantly reduce the 45°C cycle gas production, and the gas production can reach the level of the 45°C cycle gas production of the positive electrode plate with an initial low moisture content. Therefore, for some increases in moisture content caused by abnormal production lines, the lithium powder content of the positive electrode plate can be increased to suppress its 45°C cycle gas production.

[0165] When lithium powder is added to the positive electrode plate, the lithium powder will also release capacity during the electrochemical process. Therefore, under the same negative electrode surface density, the increase in lithium powder content will also cause the risk of lithium plating. Therefore, in Example 10, because the amount of passivation lithium powder added is increased, part of the passivation lithium powder will participate in the electrochemical reaction in the electrochemical process to release capacity, and lithium plating will occur at the negative electrode if the negative electrode surface density is not increased.

[0166] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0167] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that: include: Positive electrode current collector; A positive electrode active material layer is provided on at least one side of the positive electrode current collector, and lithium powder is dispersed on a side of the positive electrode active material layer away from the positive electrode current collector.

2. The positive electrode sheet according to claim 1, characterized in that: The positive electrode active material layer includes a positive electrode active material. Based on the total mass of the positive electrode active material, the amount of the lithium powder is 0.005 wt % to 5 wt %.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The D 50 5μm~40μm.

4. The positive electrode sheet according to claim 1 or 2, characterized in that: The lithium powder includes at least one of metallic lithium powder and passivation lithium powder.

5. The positive electrode sheet according to claim 4, characterized in that: The passivated lithium powder comprises metallic lithium powder and a coating layer coated on the surface of the metallic lithium powder, wherein the coating layer comprises at least one of lithium fluoride, lithium carbonate, lithium nitride, metallic cobalt and metallic silver.

6. The positive electrode sheet according to claim 5, characterized in that: Based on the total mass of the passivated lithium powder, the mass proportion of the coating layer is 2% to 30%.

7. The positive electrode sheet according to claim 1 or 2, characterized in that: The surface density of the positive electrode sheet is 300g / m 2 ~500g / m 2 and / or, The compaction density of the positive electrode sheet is 2.20 g / cm 3 ~3.6g / cm 3 .

8. A method for preparing a positive electrode sheet according to any one of claims 1 to 7, characterized in that: include: (1) applying a positive electrode slurry to at least one side of a positive electrode current collector to form a positive electrode active material layer on the positive electrode current collector; (2) Lithium powder is applied to the positive electrode active material layer on a side away from the positive electrode current collector to obtain a positive electrode sheet.

9. The method according to claim 8, characterized in that Before applying lithium powder to the positive electrode active material layer at a side away from the positive electrode current collector, the positive electrode active material layer is preliminarily subjected to a heat treatment.

10. The method according to claim 9, characterized in that The lithium powder is applied to the positive electrode active material layer on a side away from the positive electrode current collector by roller pressing.

11. A battery, characterized in that: The invention comprises the positive electrode sheet according to any one of claims 1 to 7, and / or the positive electrode sheet made by the method according to any one of claims 8 to 10.

12. The battery according to claim 11, characterized in that Also includes: The electrolyte has an injection coefficient of 2.0 g / Ah to 4.5 g / Ah.

13. An electrical device, characterized in that: A battery comprising the battery according to claim 11 or 12.

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