Positive electrode sheet, method for manufacturing the same, and battery

Abstract

The application provides a positive electrode sheet, a preparation method thereof, and a battery to improve the technical problems that the capacity of LMFP is difficult to effectively exert and the cycle life of the battery is poor. The positive electrode sheet comprises a current collector, a first active material layer and a second active material layer arranged on the current collector, and the first active material layer and the second active material layer are sequentially distributed in the direction away from the current collector; the first active material layer and the second active material layer both contain lithium manganese iron phosphate; the first active material layer further contains a first conductive agent and a first lithium supplement agent, and the second active material layer further contains a second conductive agent and a second lithium supplement agent; wherein the gram capacity K1 of the first lithium supplement agent is greater than the gram capacity K2 of the second lithium supplement agent; and the mass percentage content D1 of the first conductive agent in the first active material layer is greater than the mass percentage content D2 of the second conductive agent in the second active material layer.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode sheet, a method for preparing a positive electrode sheet, and a battery. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) is a cathode active material made by adding a certain proportion of manganese to lithium iron phosphate (LFP). Both LMFP and LFP belong to the olivine structure and have the same theoretical specific capacity. However, LMFP has a higher voltage plateau, typically around 4.1V, higher than LFP's 3.3V~3.5V. Therefore, under comparable conditions, the theoretical energy density of LMFP is 15%-20% higher than that of LFP. However, compared to LFP, LMFP has poorer electronic conductivity and lithium-ion diffusion rate, preventing it from fully utilizing its capacity; furthermore, LMFP has a poorer cycle life, especially at high temperatures compared to LFP.

[0003] To address the shortcomings of LMFPs, lithium replenishment at the cathode is necessary. However, the application of lithium replenishing agents in LMFP systems is relatively simple in related technologies, making it difficult for these agents to function effectively. Consequently, the capacity of the LMFP is not fully utilized, and the cycle life of the battery is difficult to improve. Summary of the Invention

[0004] The embodiments of this application provide a positive electrode sheet and a method for preparing the same, as well as a battery, to improve the technical problems of LMFP's ineffective capacity utilization and poor battery cycle life.

[0005] In a first aspect, embodiments of this application provide a positive electrode sheet, comprising: a current collector and a first active material layer and a second active material layer disposed on the current collector, wherein the first active material layer and the second active material layer are sequentially distributed along a direction away from the current collector; both the first active material layer and the second active material layer contain lithium manganese iron phosphate; the first active material layer further contains a first conductive agent and a first lithium replenishing agent, and the second active material layer further contains a second conductive agent and a second lithium replenishing agent; wherein the specific capacity K1 of the first lithium replenishing agent is greater than the specific capacity K2 of the second lithium replenishing agent; and the mass percentage D1 of the first conductive agent in the first active material layer is greater than the mass percentage D2 of the second conductive agent in the second active material layer.

[0006] In one embodiment, the ratio P1 of the mass percentage D2 of the second conductive agent in the second active material layer to the mass percentage D1 of the first conductive agent in the first active material layer is less than 0.78.

[0007] In one embodiment, the mass percentage content B2 of the second lithium supplement in the second active material layer is greater than the mass percentage content B1 of the first lithium supplement in the first active material layer.

[0008] In one embodiment, the ratio P2 of the mass percentage content B2 of the second lithium supplement in the second active material layer to the mass percentage content B1 of the first lithium supplement in the first active material layer is 1.25 to 6.

[0009] In one embodiment, the mass percentage content B1 of the first lithium supplement in the first active material layer is 2.0 wt% to 4.0 wt%.

[0010] In one embodiment, the mass percentage content B2 of the second lithium supplement in the second active material layer is 5.0 wt% to 15.0 wt%.

[0011] In one embodiment, the mass percentage content D1 of the first conductive agent in the first active material layer is 0.3 wt% to 1.4 wt%.

[0012] In one embodiment, the mass percentage content D2 of the second conductive agent in the second active material layer is 0.15 wt% to 0.7 wt%.

[0013] In one embodiment, the first lithium supplement includes at least one of LiNiO2 and Li5FeO4; and / or, the second lithium supplement includes a lithium-rich manganese-based material, and the chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2, where 0 < x < 1, and M includes at least one transition metal.

[0014] In one embodiment, the initial charge calibrated specific capacity of the first lithium supplement is greater than 300 mAh / g; and / or, the initial charge calibrated specific capacity of the second lithium supplement is greater than 100 mAh / g.

[0015] In one embodiment, the mass percentage content H1 of lithium iron phosphate manganese in the first active material layer is 91.0 wt% to 95.3 wt%.

[0016] In one embodiment, the mass percentage content H2 of lithium iron phosphate manganese in the second active material layer is 80.0 wt% to 92.55 wt%.

[0017] In one embodiment, both the first active material layer and the second active material layer further include a binder. The content N1 of the binder in the first active material layer is 1.5 wt% to 2.0 wt%, and / or, the content N2 of the binder in the second active material layer is 1.5 wt% to 2.0 wt%.

[0018] In one embodiment, both the first active material layer and the second active material layer further comprise a dispersant, wherein the content of the dispersant F1 in the first active material layer is 0.1wt%~0.2wt%, and / or the content of the dispersant F2 in the second active material layer is 0.1wt%~0.2wt%.

[0019] Secondly, embodiments of this application provide a method for preparing a positive electrode sheet, the method comprising:

[0020] Prepare a first slurry, the first slurry comprising lithium manganese iron phosphate, a first conductive agent and a first lithium replenishing agent;

[0021] A second slurry is prepared, the second slurry comprising lithium manganese iron phosphate, a second conductive agent, and a second lithium supplementing agent;

[0022] The first slurry is subjected to film formation treatment on the current collector to obtain the first active material layer;

[0023] The second slurry is deposited on the side of the first active material layer away from the current collector to form a second active material layer.

[0024] Thirdly, embodiments of this application provide a battery including the above-described positive electrode sheet; or, a positive electrode sheet prepared by the above method.

[0025] The beneficial effects of the embodiments of this application are as follows:

[0026] In the embodiments of this application, by designing the active material layers in the positive electrode sheet in layers, the first active material layer near the current collector has a relatively large specific capacity of the first lithium replenishing agent and a relatively high mass percentage of the first conductive agent, while the second active material layer far from the current collector has a relatively small specific capacity of the second lithium replenishing agent and a relatively low mass percentage of the second conductive agent. In this way, under the same mass, the first lithium replenishing agent can provide more lithium ions than the second conductive agent, and compared with the second active material layer, the first active material layer has a denser conductive network. Therefore, during the battery formation process (i.e., the first charge and discharge process), when the first lithium replenishing agent can release a large number of lithium ions to the negative electrode, it has a lower lithium ion diffusion resistance, optimizes lithium ion transport, and thus promotes the utilization of the capacity of lithium manganese iron phosphate in the positive electrode sheet, especially the capacity of lithium manganese iron phosphate in the part of the positive electrode sheet near the current collector, thereby improving the cycle life of the lithium-ion battery. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic cross-sectional view of the positive electrode sheet provided in an embodiment of this application.

[0029] Figure label:

[0030] 10. Positive electrode sheet; 11. Current collector; 12. First active material layer; 13. Second active material layer. Detailed Implementation

[0031] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] Furthermore, it should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operation, specifically the directions shown in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0033] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0035] The terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0036] In the description of the embodiments of this application, the words "example" or "for example" are used to indicate exemplification, illustration, or description. Any embodiment or design described as "example" or "for example" in the embodiments of this application is not to be construed as being more preferred or having more advantages than another embodiment or design. The use of the words "example" or "for example" is intended to present relative concepts in a clear manner.

[0037] To facilitate understanding of the present application, the spline curves and arrows used in the reference numerals in the accompanying drawings are explained below: spline curves without arrows indicate solid parts, that is, parts with solid structures; spline curves with arrows indicate virtual parts, that is, parts without solid structures.

[0038] Firstly, please see Figure 1 This application provides a positive electrode 10, which is used in a battery, such as a lithium-ion battery.

[0039] Specifically, the positive electrode 10 includes a current collector 11, a first active material layer 12, and a second active material layer 13. The first active material layer 12 and the second active material layer 13 are disposed on the current collector 11 and are sequentially distributed along a direction away from the current collector 11. Both the first active material layer 12 and the second active material layer 13 contain the positive electrode active material lithium manganese iron phosphate (LMFP). The first active material layer 12 also contains a first conductive agent and a first lithium replenishing agent, and the second active material layer 13 also contains a second conductive agent and a second lithium replenishing agent. The specific capacity K1 of the first lithium replenishing agent is greater than the specific capacity K2 of the second lithium replenishing agent; the mass percentage D1 of the first conductive agent in the first active material layer 12 is greater than the mass percentage D2 of the second conductive agent in the second active material layer 13.

[0040] The chemical formula of lithium manganese iron phosphate is LiFe a Mn bPO4, where 0 < a < 1 and 0 < b < 1. As an example, a can be 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.999; b can be 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.999.

[0041] The lithium supplement can compensate for the irreversible lithium loss during the first charge and discharge process. The specific capacity of the lithium supplement refers to the capacity provided by each gram of the lithium supplement in the battery, usually expressed in mAh / g. The specific capacity of the lithium supplement varies depending on the specific composition.

[0042] As an example, lithium ferrite (LFO) is a lithium metal oxide with an antifluorite structure. The chemical formula of lithium ferrite is Li5FeO4, and its theoretical specific capacity can reach 700 mAh / g. <​​​​​​​​​​​​​​​In the embodiment of the present application, the positive electrode sheet 10 is provided with a hierarchical design for the active material layer. Among them, in the first active material layer 12 close to the current collector 11, the gram capacity of the first lithium supplement agent is relatively large, and the mass percentage content of the first conductive agent is relatively high. While in the second active material layer 13 far from the current collector 11, the gram capacity of the second lithium supplement agent is relatively small, and the mass percentage content of the second conductive agent is relatively low. In this way, under the same mass, the first lithium supplement agent can provide more lithium ions than the second conductive agent, and compared with the second active material layer 13, the first active material layer 12 has a denser conductive network. Therefore, during the battery formation process (i.e., the first charge-discharge process), when the first lithium supplement agent can release a large amount of lithium ions to the negative electrode, it has a lower lithium ion diffusion resistance, optimizes the transmission of lithium ions, and further promotes the capacity utilization of lithium iron phosphate manganese in the positive electrode sheet 10, especially the capacity utilization of lithium iron phosphate manganese in the first active material layer 12, improving the capacity and cycle life of the battery.

[0049] In some embodiments, the first lithium supplement agent includes at least one of LiNiO2 and Li5FeO4. LiNiO2 and Li5FeO4 have a relatively high gram capacity. In a lithium iron phosphate manganese system battery, adding a small amount of LiNiO2 and / or Li5FeO4 can effectively improve the energy density of the battery. However, LiNiO2 and Li5FeO4 are unstable. They not only have strong water absorption characteristics but are also prone to decomposition when exposed to air for a long time. By adding LiNiO2 and / or Li5FeO4 to the first active material layer 12 and using the current collector 11 and the second active material layer 13 to shield the first active material layer 12, water vapor can be effectively isolated, reducing the risk of inactivation of LiNiO2 and / or Li5FeO4. Optionally, the first lithium supplement agent includes LNO. Compared with LFO, LNO has more stable properties and can more effectively promote the capacity utilization of lithium iron phosphate manganese.

[0050] In some embodiments, the second lithium supplement agent includes a lithium-rich manganese-based material. The chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiMO2, where 0 < x < 1, and M includes at least one transition metal. Although the gram capacity of the lithium-rich manganese-based material is not as high as that of LiNiO2 and Li5FeO4, the lithium-rich manganese-based material is relatively stable, and the price of the lithium-rich manganese-based material is relatively low, which is beneficial to controlling the production cost of the battery. As an example, x is 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.999. M includes at least one of Ni, Co, and Mn.

[0051] In some embodiments, the ratio P1 of the mass percentage D2 of the second conductive agent in the second active material layer 13 to the mass percentage D1 of the first conductive agent in the first active material layer 12 is less than 0.78. This allows for further optimization of the conductive system while maintaining the total amount of conductive agent, promoting the effective functioning of the lithium supplement. Optionally, P1 is less than 0.67. As examples, P1 is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or 0.67.

[0052] In some embodiments, the mass percentage D1 of the first conductive agent in the first active material layer 12 is 0.3wt% to 1.4wt%. As examples, D1 is 0.3wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.3wt%, or 1.4wt%.

[0053] In some embodiments, the mass percentage D2 of the second conductive agent in the second active material layer 13 is 0.15wt% to 0.7wt%. As examples, D2 is 0.15wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, or 0.7wt%.

[0054] In some embodiments, the mass percentage B2 of the second lithium replenishing agent in the second active material layer 13 is greater than the mass percentage B1 of the first lithium replenishing agent in the first active material layer 12. Compared to the first active material layer 12, the second active material layer 13 is closer to the surface of the positive electrode 10, thus the lithium ion transport path released by the second lithium replenishing agent is shorter and the diffusion resistance is lower. By increasing the mass percentage B2 of the second lithium replenishing agent in the second active material layer 13, the overall lithium ion transport in the positive electrode 10 can be further optimized.

[0055] In some embodiments, the ratio P2 of the mass percentage of the second lithium replenishing agent B2 in the second active material layer 13 to the mass percentage of the first lithium replenishing agent B1 in the first active material layer 12 is 1.25 to 6. Within this range, the capacity of lithium manganese iron phosphate in both the first active material layer 12 and the second active material layer 13 can be effectively utilized, thereby improving the battery capacity and cycle life. As examples, P2 is 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6.

[0056] In some embodiments, the mass percentage of the first lithium supplementer B1 in the first active material layer 12 is 2.0 wt% to 4.0 wt%. As an example, B1 is 2.0 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3.0 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, or 4.0 wt%.

[0057] In some embodiments, the mass percentage of the second lithium supplementer B2 in the second active material layer 13 is 5.0 wt% to 15.0 wt%. As examples, B2 is 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, 10.0 wt%, 10.5 wt%, 11.0 wt%, 11.5 wt%, 12.0 wt%, 12.5 wt%, 13.0 wt%, 13.5 wt%, 14.0 wt%, 14.5 wt%, or 15.0 wt%.

[0058] In some implementations, the first lithium replenisher has an initial charge calibrated capacity greater than 300 mAh / g, and the second lithium replenisher has an initial charge calibrated capacity greater than 100 mAh / g. The initial charge calibrated capacity, also known as the first charge capacity, refers to the ratio of the capacity released by the lithium replenisher during the first charge of the lithium-ion battery to the mass of the lithium replenisher. The initial charge calibrated capacity of the lithium replenisher is only related to the type of lithium replenisher material; that is, once the type of lithium replenisher material is determined, the initial charge calibrated capacity is a fixed value, meaning it is an inherent property of the lithium replenisher itself. For example, the first lithium replenisher includes at least one of LFO and LNO, with LFO having an initial charge calibrated capacity of 590 mAh / g and LNO having an initial charge calibrated capacity of 350 mAh / g. For example, the second lithium replenisher includes LMR, with LMR having an initial charge calibrated capacity of 140 mAh / g.

[0059] In some embodiments, the mass percentage H1 of lithium manganese iron phosphate in the first active material layer 12 is 91.0 wt% to 95.3 wt%. Within this range, the energy density of the battery can be effectively guaranteed. As examples, H1 is 91.0 wt%, 92.0 wt%, 93.0 wt%, 94.0 wt%, or 95.3 wt%.

[0060] In some embodiments, the mass percentage (H2) of lithium manganese iron phosphate in the second active material layer 13 is 80.0 wt% to 92.55 wt%. Within this range, the energy density of the battery can be effectively guaranteed. As examples, H2 is 80.0 wt%, 82.0 wt%, 84.0 wt%, 86.0 wt%, 88.0 wt%, 90.0 wt%, or 92.55 wt%.

[0061] In some embodiments, both the first active material layer 12 and the second active material layer 13 further comprise an adhesive. Optionally, the adhesive comprises at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), and polyvinyl alcohol (PVA).

[0062] In some embodiments, the binder content N1 in the first active material layer 12 is 1.5 wt% to 2.0 wt%, and the binder content N2 in the second active material layer 13 is 1.5 wt% to 2.0 wt%. As examples, N1 is 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%; and N2 is 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%.

[0063] In some embodiments, both the first active material layer 12 and the second active material layer 13 further comprise a dispersant. Optionally, the dispersant includes at least one selected from acid anhydrides, polyvinylpyrrolidone, sulfate salts, poly(N-vinylacetamide), polyvinyl alcohol, sulfonates, and polyethylene glycol.

[0064] In some embodiments, the content of dispersant F1 in the first active material layer 12 is 0.1wt% to 0.2wt%, and the content of dispersant F2 in the second active material layer 13 is 0.1wt% to 0.2wt%. As an example, F1 is 0.1wt%, 0.12wt%, 0.14wt%, 0.16wt%, 0.18wt%, or 0.2wt%; and F2 is 0.1wt%, 0.12wt%, 0.14wt%, 0.16wt%, 0.18wt%, or 0.2wt%.

[0065] In some embodiments, the current collector 11 can be an aluminum foil, a carbon-coated aluminum foil, a safety-coated aluminum foil, an etched aluminum foil, or an aluminum mesh. The thickness of the current collector 11 can be 5μm to 20μm, for example, 5μm, 10μm, 15μm, or 20μm.

[0066] Secondly, embodiments of this application also provide a method for preparing a positive electrode sheet, used to prepare the above-mentioned positive electrode sheet 10, comprising:

[0067] S1. Prepare a first slurry, the first slurry comprising lithium manganese iron phosphate, a first conductive agent and a first lithium replenishing agent;

[0068] S2. Prepare a second slurry, the second slurry comprising lithium manganese iron phosphate, a second conductive agent, and a second lithium supplementing agent;

[0069] S3. The first slurry is subjected to film formation treatment on the current collector to obtain the first active material layer;

[0070] S4. The second slurry is subjected to film formation treatment on the side of the first active material layer away from the current collector to obtain the second active material layer.

[0071] In some embodiments, the first slurry further includes a first solvent, and S3 includes:

[0072] S31. The first slurry is coated on the current collector to obtain a first wet film layer;

[0073] S32. The first wet film layer is dried to obtain the first active material layer.

[0074] In some embodiments, the second slurry further includes a second solvent, and S4 includes:

[0075] S41. The second slurry is coated on the first wet film layer to obtain the second wet film layer;

[0076] S42. The second wet film layer is dried to obtain the second active material layer.

[0077] Optionally, the coating process includes, but is not limited to, at least one of gravure coating, microgravure coating, spray coating, and electrospinning techniques. The first solvent and the second solvent include N-methylpyrrolidone (NMP).

[0078] Thirdly, embodiments of this application also provide a battery, including the above-described positive electrode 10; or, a positive electrode prepared by the above method.

[0079] In some implementations, the battery is a lithium-ion battery.

[0080] The following description is based on specific embodiments.

[0081] Example 1

[0082] S1. Preparation of positive electrode: The positive electrode slurry is coated onto the carbon-coated aluminum foil current collector in two layers with the same density on the upper and lower layers. After drying, it is cold-pressed into sheets.

[0083] The positive electrode slurry formulation is as follows:

[0084] 1. Upper layer slurry: LMFP (LiFe 0.5 Mn 0.5 PO4 (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), and dispersant (0.2wt%), wherein LMR: 0.6Li2MnO3·0.4LiNiO2, is added simultaneously with LMFP during stirring, and LMR is the lithium replenishing agent in the upper layer.

[0085] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0086] S2. Preparation of negative electrode: The negative electrode slurry is coated onto copper foil in a single layer, and after drying, it is cold-pressed into sheets.

[0087] The negative electrode slurry formulation is: graphite:SP:CMC:SBR=96.7:0.6:1.2:1.5 (mass ratio).

[0088] S3. Battery preparation: The positive and negative electrode sheets are stacked to assemble the core pack. After assembly, the core pack is vacuum baked. After baking, the moisture content is qualified, and the core pack is injected with liquid (1M LiPF6 (EC:DEC:DMC=1:1:1, volume ratio)). After the liquid injection is completed, the core pack is left to stand for 24 hours to improve its capacity. After the capacity is improved, the core pack is vacuum sealed and the soft-pack cell is off the production line.

[0089] Example 2

[0090] The difference from Example 1 lies in the positive electrode slurry formulation:

[0091] 1. Upper layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer;

[0092] 2. Lower layer slurry: LMFP (94.7wt%), LNO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LNO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0093] Everything else is the same as in Example 1.

[0094] Example 3

[0095] The difference from Example 1 lies in the positive electrode slurry formulation:

[0096] 1. Upper layer slurry: LMFP (90.95wt%), LMR (7wt%), SP (0.1wt%), CNT (0.05wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0097] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0098] Everything else is the same as in Example 1.

[0099] Example 4

[0100] The difference from Example 1 lies in the positive electrode slurry formulation:

[0101] 1. Upper layer slurry: LMFP (90.5wt%), LMR (7wt%), SP (0.4wt%), CNT (0.2wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0102] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0103] Everything else is the same as in Example 1.

[0104] Example 5

[0105] The difference from Example 1 lies in the positive electrode slurry formulation:

[0106] 1. Upper layer slurry: LMFP (90.4wt%), LMR (7wt%), SP (0.45wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0107] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0108] Everything else is the same as in Example 1.

[0109] Example 6

[0110] The difference from Example 1 lies in the positive electrode slurry formulation:

[0111] 1. Upper layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0112] 2. Lower layer slurry: LMFP (94.89wt%), LFO (2.5wt%), SP (0.5wt%), CNT (0.21wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0113] Everything else is the same as in Example 1.

[0114] Example 7

[0115] The difference from Example 1 lies in the positive electrode slurry formulation:

[0116] 1. Upper layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0117] 2. Lower layer slurry: LMFP (94.5wt%), LFO (2.5wt%), SP (0.8wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during the stirring process, and LFO is the lithium supplement for the lower layer.

[0118] Everything else is the same as in Example 1.

[0119] Example 8

[0120] The difference from Example 1 lies in the positive electrode slurry formulation:

[0121] 1. Upper layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0122] 2. Lower layer slurry: LMFP (94.2wt%), LFO (2.5wt%), SP (0.9wt%), CNT (0.5wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as a lithium supplement for the lower layer.

[0123] Everything else is the same as in Example 1.

[0124] Example 9

[0125] The difference from Example 1 lies in the positive electrode slurry formulation:

[0126] 1. Upper layer slurry: LMFP (90.95wt%), LMR (7wt%), SP (0.1wt%), CNT (0.05wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0127] 2. Lower layer slurry: LMFP (95.3wt%), LFO (2.5wt%), SP (0.2wt%), CNT (0.1wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0128] Everything else is the same as in Example 1.

[0129] Example 10

[0130] The difference from Example 1 lies in the positive electrode slurry formulation:

[0131] 1. Upper layer slurry: LMFP (90.4wt%), LMR (7wt%), SP (0.5wt%), CNT (0.2wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0132] 2. Lower layer slurry: LMFP (94.4wt%), LFO (2.5wt%), SP (0.9wt%), CNT (0.5wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during the stirring process, and LFO is the lithium supplement for the lower layer.

[0133] Everything else is the same as in Example 1.

[0134] Example 11

[0135] The difference from Example 1 lies in the positive electrode slurry formulation:

[0136] 1. Upper layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0137] 2. Lower layer slurry: LMFP (93.2wt%), LFO (4.0wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during the stirring process, and LFO is the lithium supplement for the lower layer.

[0138] Everything else is the same as in Example 1.

[0139] Example 12

[0140] The difference from Example 1 lies in the positive electrode slurry formulation:

[0141] 1. Upper layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0142] 2. Lower layer slurry: LMFP (95.2wt%), LFO (2.0wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LFO is added simultaneously with LMFP during the stirring process, and LFO is the lithium supplement for the lower layer.

[0143] Everything else is the same as in Example 1.

[0144] Example 13

[0145] The difference from Example 1 lies in the positive electrode slurry formulation:

[0146] 1. Upper layer slurry: LMFP (92.55wt%), LMR (5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0147] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0148] Everything else is the same as in Example 1.

[0149] Example 14

[0150] The difference from Example 1 lies in the positive electrode slurry formulation:

[0151] 1. Upper layer slurry: LMFP (85.05wt%), LMR (12.5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0152] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0153] Everything else is the same as in Example 1.

[0154] Example 15

[0155] The difference from Example 1 lies in the positive electrode slurry formulation:

[0156] 1. Upper layer slurry: LMFP (82.55wt%), LMR (15wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0157] 2. Lower layer slurry: LMFP (94.7wt%), LFO (2.5wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0158] Everything else is the same as in Example 1.

[0159] Example 16

[0160] The difference from Example 1 lies in the positive electrode slurry formulation:

[0161] 1. Upper layer slurry: LMFP (92.55wt%), LMR (5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0162] 2. Lower layer slurry: LMFP (93.9wt%), LFO (3.3wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the lower layer.

[0163] Everything else is the same as in Example 1.

[0164] Example 17

[0165] The difference from Example 1 lies in the positive electrode slurry formulation:

[0166] 1. Upper layer slurry: LMFP (92.55wt%), LMR (5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0167] 2. Lower layer slurry: LMFP (93.2wt%), LFO (4wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as a lithium supplement for the lower layer.

[0168] Everything else is the same as in Example 1.

[0169] Example 18

[0170] The difference from Example 1 lies in the positive electrode slurry formulation:

[0171] 1. Upper layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer;

[0172] 2. Lower layer slurry: LMFP (94.7wt%), LFO (1.25wt%), LNO (1.25wt%), SP (0.6wt%), CNT (0.3wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LNO and LFO are added simultaneously with LMFP during the stirring process, and LNO and LFO are lithium supplementers for the lower layer.

[0173] Everything else is the same as in Example 1.

[0174] Comparative Example 1

[0175] The difference from Example 6 lies in step S1 (preparation of the positive electrode):

[0176] The positive electrode slurry is coated onto a carbon-coated aluminum foil current collector in a single layer, and after drying, it is cold-pressed into sheets.

[0177] The positive electrode slurry formulation is as follows: LMFP (92.72wt%), LMR (4.75wt%), SP (0.35wt%), CNT (0.28wt%), PVDF (1.7wt%), and dispersant (0.2wt%). LMR and LMFP are added simultaneously during the stirring process, and LMR is a lithium supplement agent.

[0178] Everything else is the same as in Example 1.

[0179] Comparative Example 2

[0180] The difference from Example 6 lies in step S1 (preparation of the positive electrode):

[0181] The positive electrode slurry is coated onto a carbon-coated aluminum foil current collector in a single layer, and after drying, it is cold-pressed into sheets.

[0182] The positive electrode slurry formulation is as follows: LMFP (92.72wt%), LFO (4.75wt%), SP (0.35wt%), CNT (0.28wt%), PVDF (1.7wt%), and dispersant (0.2wt%). LFO is added simultaneously with LMFP during the stirring process and serves as a lithium supplement.

[0183] Everything else is the same as in Example 1.

[0184] Comparative Example 3

[0185] The difference from Example 6 lies in the positive electrode slurry formulation:

[0186] 1. Upper layer slurry: LMFP (90.47wt%), LMR (7wt%), SP (0.35wt%), CNT (0.28wt%), PVDF (1.7wt%), dispersant (0.2wt%), wherein LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer;

[0187] 2. Lower layer slurry: LMFP (94.97wt%), LFO (2.5wt%), SP (0.35wt%), CNT (0.28wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as a lithium supplement for the lower layer.

[0188] Everything else is the same as in Example 1.

[0189] Comparative Example 4

[0190] The difference from Example 6 lies in the positive electrode slurry formulation:

[0191] 1. Upper layer slurry: LMFP (90.39wt%), LMR (7wt%), SP (0.5wt%), CNT (0.21wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the upper layer.

[0192] 2. Lower layer slurry: LMFP (95.05wt%), LFO (2.5wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as a lithium supplement for the lower layer.

[0193] Everything else is the same as in Example 1.

[0194] Comparative Example 5

[0195] The difference from Example 6 lies in the positive electrode slurry formulation:

[0196] 1. Upper layer slurry: LMFP (94.89wt%), LFO (2.5wt%), SP (0.5wt%), CNT (0.21wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LFO is added simultaneously with LMFP during stirring and serves as the lithium supplement for the upper layer.

[0197] 2. Lower layer slurry: LMFP (90.55wt%), LMR (7wt%), SP (0.3wt%), CNT (0.25wt%), PVDF (1.7wt%), dispersant (0.2wt%), where LMR and LMFP are added simultaneously during stirring, and LMR is the lithium supplement for the lower layer.

[0198] Everything else is the same as in Example 1.

[0199] The parameters of each embodiment and comparative example are recorded in Table 1.

[0200] Table 1

[0201]

[0202] The content of each material in Table 1 is in wt%.

[0203] The batteries prepared in the examples and comparative examples were tested as follows:

[0204] 1. Specific capacity test: At 25℃, the battery is charged at a rate of 0.33C, and then discharged at 0.33C after being fully charged. The discharge capacity is obtained, and the specific capacity is calibrated. The results are recorded in Table 2.

[0205] 2. Capacity retention test: The battery was subjected to a 1C / 1C cycle test at 25℃. The capacity retention rate was calculated by dividing the capacity after 500 cycles by the initial capacity. The test results are recorded in Table 2.

[0206] 3. DC internal resistance (DCR) growth rate test: DCR test was performed at 1C@10s 70% SOC DCR; at 25℃, the battery was subjected to 1C / 1C cycle test. The DCR growth rate was calculated by dividing the difference between the DCR and the initial DCR after 500 cycles by the initial DCR. The test results are recorded in Table 2.

[0207] Table 2

[0208]

[0209] The results in Table 2 show that:

[0210] The batteries provided in Examples 1 to 18 maintain a specific capacity of 139.6 mAh / g or higher, a capacity retention of 95.3% or higher, and a DCR growth rate of 8.9% or lower.

[0211] Further comparisons were made with Example 6 and Comparative Examples 1 to 5. Under the condition that the total content of each material in the electrode was the same, compared with Comparative Examples 1 and 2 (the positive electrode has only a single layer of active material, and the lithium replenisher is simply mixed in the active material layer), Comparative Example 3 (the active material layers are layered, but the conductive agent content in the upper and lower active material layers is the same), Comparative Example 4 (the active material layers are layered, but the conductive agent content in the lower active material layer is less than that in the upper layer), and Comparative Example 5 (the active material layers are layered, but the conductive agent content in the lower active material layer is less than that in the upper layer, and the specific capacity of the lithium replenisher in the upper layer is greater than that in the lower layer), Example 6 showed improved specific capacity and capacity retention, while reducing the DCR growth rate. This indicates that by layering the active material layers, with the specific capacity of the lithium replenisher in the inner layer being greater than that in the outer layer, and the content of the conductive agent in the inner layer being greater than that in the outer layer, the capacity of the LMFP in the active material layer can be effectively promoted, improving the cycle stability of the battery, reducing the DC internal resistance growth rate of the battery, and improving the battery performance.

[0212] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode plate, characterized in that, Comprising: A current collector, a first active material layer and a second active material layer provided on the current collector, the first active material layer and the second active material layer are sequentially distributed along the direction away from the current collector; both the first active material layer and the second active material layer contain lithium iron phosphate manganese; the first active material layer further contains a first conductive agent and a first lithium supplementing agent, and the second active material layer further contains a second conductive agent and a second lithium supplementing agent; wherein, the gram capacity K1 of the first lithium supplementing agent is greater than the gram capacity K2 of the second lithium supplementing agent; the mass percentage content D1 of the first conductive agent in the first active material layer is greater than the mass percentage content D2 of the second conductive agent in the second active material layer; the ratio P1 of the mass percentage content D2 of the second conductive agent in the second active material layer to the mass percentage content D1 of the first conductive agent in the first active material layer is less than 0.78; the ratio P2 of the mass percentage content B2 of the second lithium supplementing agent in the second active material layer to the mass percentage content B1 of the first lithium supplementing agent in the first active material layer is 1.25 - 6.

2. The positive electrode sheet according to claim 1, characterized in that, The mass percentage content B1 of the first lithium supplementing agent in the first active material layer is 2.0wt% - 4.0wt%; and / or, The mass percentage content B2 of the second lithium supplementing agent in the second active material layer is 5.0wt% - 15.0wt%.

3. The positive electrode sheet according to claim 1, characterized in that, The mass percentage content D1 of the first conductive agent in the first active material layer is 0.3wt% - 1.4wt%; and / or, The mass percentage content D2 of the second conductive agent in the second active material layer is 0.15wt% - 0.7wt%.

4. The positive electrode sheet according to claim 1, characterized in that, The first lithium supplementing agent includes at least one of LiNiO2 and Li5FeO4; and / or, the second lithium supplementing agent includes a lithium-rich manganese-based material, and the chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiMO2, where 0 < x < 1, and M includes at least one transition metal.

5. The positive electrode sheet according to claim 1, characterized in that, The first charge calibration gram capacity of the first lithium supplementing agent is greater than 300mAh / g; and / or, the first charge calibration gram capacity of the second lithium supplementing agent is greater than 100mAh / g.

6. The positive electrode sheet according to claim 1, characterized in that, The mass percentage content H1 of the lithium iron phosphate manganese in the first active material layer is 91.0wt% - 95.3wt%; and / or, The mass percentage content H2 of the lithium iron phosphate manganese in the second active material layer is 80.0wt% - 92.55wt%.

7. The positive electrode sheet according to claim 1, characterized in that, Both the first active material layer and the second active material layer further contain a binder, the content N1 of the binder in the first active material layer is 1.5wt% - 2.0wt%, and / or, the content N2 of the binder in the second active material layer is 1.5wt% - 2.0wt%.

8. The positive electrode sheet according to claim 1, characterized in that, Both the first active material layer and the second active material layer further contain a dispersant, the content F1 of the dispersant in the first active material layer is 0.1wt% - 0.2wt%, and / or, the content F2 of the dispersant in the second active material layer is 0.1wt% - 0.2wt%.

9. A method for preparing a positive electrode sheet, used to prepare the positive electrode sheet as described in any one of claims 1 to 8, characterized in that, Comprising: Prepare a first slurry, the first slurry comprising lithium manganese iron phosphate, a first conductive agent and a first lithium replenishing agent; A second slurry is prepared, the second slurry comprising lithium manganese iron phosphate, a second conductive agent, and a second lithium supplementing agent; The first slurry is subjected to film formation treatment on the current collector to obtain the first active material layer; The second slurry is deposited on the side of the first active material layer away from the current collector to form a second active material layer.

10. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1 to 8; or, the positive electrode sheet prepared by the method as described in claim 9.

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