Positive lithium supplement binder, positive slurry, positive plate and battery

Abstract

The invention relates to a positive electrode lithium supplement binder, a positive electrode slurry, a positive plate and a battery, the positive electrode lithium supplement binder is characterized by comprising PVDF (Polyvinylidene Fluoride) 5130, PAA (Polyacrylic Acid) and PVDF 900, and the mass ratio of the PVDF 5130 to the PAA to the PVDF 900 is (1-1.6): (0.2-0.4): (0.2-0.6). When the positive electrode slurry is used in combination with the lithium supplement agent, the gel problem of the positive electrode slurry can be further solved remarkably by adopting the combination of PVDF 5130, PAA and PVDF 900 and simultaneously using the combination of VDF 5130, PAA and PVDF 900, and the slurry agglomeration problem can also be solved, so that the electric specific capacity of the positive electrode can be improved, and the discharge specific capacity of the positive electrode can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of battery lithium replenishment, and in particular to a positive electrode lithium replenishment binder, a positive electrode slurry, a positive electrode sheet and a battery. Background Art

[0002] Lithium-ion battery is a secondary battery system in which the positive electrode active material provides a reversible lithium source and the negative electrode acts as a carrier, producing a reversible reaction through the potential difference between different substances. With its advantages of high specific capacity, long cycle life, and low self-discharge, it is widely used in mobile phones, portable electronic devices and other fields. Large-capacity long-cycle lithium-ion batteries have been used in electric vehicles and energy storage power stations. However, during the first charge and discharge process, lithium ions, which are the positive electrode active material, will form a layer of SEI on the surface of the negative electrode, consuming about 10% of the lithium ions in the positive electrode active material. The lithium ions at this stage are irreversible, resulting in the initial efficiency of the positive electrode to only reach 90%, or even lower. At the same time, during the cycle process, SEI will repeatedly decompose and repair, and will also continuously consume lithium from the positive electrode active material. The effective utilization rate of lithium continues to decrease. In order to make up for the above lithium loss, lithium supplements came into being. Especially in recent years, positive electrode lithium replenishers such as Li5FeO4 and Li2NiO2 have emerged. A small amount of addition can make up for the loss of lithium ions in the first charge. However, during the preparation process of Li5FeO4, Li2NiO2 and other substances, residual alkalis such as LiOH and LiCO3 will exist on the surface. In addition, the lithium replenisher can easily react with H2O and CO2 in the air, which aggravates the production of alkaline substances. Once the amount of addition increases, under the existing system, during the lithium battery positive electrode slurrying process, the alkaline substances in the lithium replenisher undergo dehydrogenation and fluorination through nucleophilic reaction with PVDF to form a cross-linked conjugated polyene, which leads to dehydrogenation and fluorination (gelation) of the PVDF molecular chain, making it impossible to use it on a large scale and in large doses.

[0003] CN117059810A discloses a lithium-supplementing binder and a lithium-supplementing positive electrode slurry and a preparation method thereof and a lithium-ion battery. The lithium-supplementing binder includes polyvinylidene fluoride PVDF and a polypropylene compound; the polypropylene compound is polyacrylonitrile PAN or polyacrylic acid PAA. The technical solution of the present application introduces a part of fluorine-free glue into the lithium-supplementing binder of the positive electrode, which can significantly improve the gelation phenomenon of the slurry and improve the fluidity of the slurry. However, the positive electrode sheet prepared by the fluorine-free glue is relatively brittle and cannot be completely replaced. The retained part of the fluorine-containing PVDF glue can ensure the flexibility of the electrode sheet and reduce the impedance. However, when polyvinylidene fluoride PVDF and polyacrylic acid PAA are used as a combined binder, the problem of slurry agglomeration is still very easy to occur during the configuration of the positive electrode slurry, which affects the coating of the positive electrode slurry, resulting in a lower positive charge specific capacity and a lower positive discharge specific capacity. Summary of the invention

[0004] Based on this, it is necessary to provide a positive electrode lithium replenishing binder, positive electrode slurry, positive electrode sheet and battery that can solve the gel problem of positive electrode slurry, solve the slurry agglomeration problem, improve the positive electrode charge capacity and improve the positive electrode discharge capacity.

[0005] In a first aspect, the present application provides a positive electrode lithium supplement binder, characterized in that it includes PVDF5130, PAA and PVDF900, wherein the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6".

[0006] In one embodiment, the mass ratio of the PVDF5130, the PAA and the PVDF900 is 1.4:0.2:0.4.

[0007] In a second aspect, the present application further provides a positive electrode slurry, comprising a positive electrode main material, a lithium replenisher, a conductive agent, a solvent, and a positive electrode lithium replenisher binder as described in any of the above embodiments.

[0008] In one embodiment, the positive electrode main material is lithium iron phosphate, the lithium supplement agent is at least one of Li2NiO2 and Li5FeO, the conductive agent is SP, the solvent is NMP, and the mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is "86-95": "1-10": 2: "1-1.6": "0.2-0.4": "0.2-0.6".

[0009] In one embodiment, the mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is 86:10:2:1.4:0.2:0.4.

[0010] In a third aspect, the present application further provides a positive electrode sheet, comprising a current collector and a positive electrode active layer located on the current collector, wherein the positive electrode active layer comprises a lithium replenisher and the positive electrode lithium replenisher binder as described in any of the above embodiments.

[0011] In one embodiment, the positive electrode active layer further includes a positive electrode main material and a conductive agent, the positive electrode main material is lithium iron phosphate; and / or the lithium supplement agent is at least one of Li2NiO2 and Li5FeO; and / or the conductive agent is SP.

[0012] In one of the embodiments, the mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is "86-95": "1-10": 2: "1-1.6": "0.2-0.4": "0.2-0.6".

[0013] In one embodiment, the mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is 86:10:2:1.4:0.2:0.4.

[0014] In a fourth aspect, the present application also provides a lithium battery, comprising a positive electrode sheet as described in any of the above embodiments.

[0015] The present application adopts the above-mentioned positive electrode lithium replenishing binder, and when used in combination with the lithium replenishing agent, by adopting a combination of PVDF5130, PAA and PVDF900, and the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6", relative to the use of any one or any two of PVDF5130, the PAA and the PVDF900 alone, by using the combination of VDF5130, PAA and PVDF900 at the same time, the gel problem of the positive electrode slurry can be significantly further solved, and the slurry agglomeration problem can also be solved, which is beneficial to improve the positive electrode electrical specific capacity and the positive electrode discharge specific capacity. The applicant has found that the positive electrode charge specific capacity can reach more than 164mAh / g, and the positive electrode discharge specific capacity can reach more than 154mAh / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow photograph of the positive electrode slurry in Comparative Example 1;

[0017] Figure 2 This is a flow photograph of the positive electrode slurry of Example 1;

[0018] Figure 3 This is a photo of the positive electrode sheet made in Example 1;

[0019] Figure 4 This is a photo of the positive electrode sheet made in Example 1 after being folded in half;

[0020] Figure 5 The charge and discharge data and curve diagram of the test of Example 1.

[0021] Figure 6 The charge and discharge data and curve diagram of the test of comparative example 1. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of the present application, in order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application, and the preferred implementation methods of the present application are given in the accompanying drawings. However, the present application can be implemented in many different forms and is not limited to the implementation methods described herein. On the contrary, the purpose of providing these implementation methods is to make the disclosure of the present application more thoroughly and comprehensively understood. The present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited to the specific embodiments disclosed below. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present application. The terms used herein are only for the purpose of describing specific implementation methods and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0023] In a first aspect, the present application provides a positive electrode lithium supplement binder, characterized in that it includes PVDF5130, PAA and PVDF900, wherein the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6".

[0024] It should be noted that the alkaline substances in the positive electrode material may damage the PVDF structure, which is one of the main reasons for the gelation of the slurry. By combining PVDF5130, PAA and PVDF900, a more stable chemical structure may be formed, which enhances the overall alkali resistance of the binder, thereby reducing the damage of the binder structure by alkaline substances and reducing the risk of gelation. This application optimizes the binder by using a combination of PVDF5130, PAA and PVDF900, and adopts a mass ratio of the PVDF5130, the PAA and the PVDF900 of "1-1.6": "0.2-0.4": "0.2-0.6" to optimize the synergistic effect of the additives. PAA, as a polymer additive, has the effect of improving the fluidity of the slurry. PAA optimizes the viscosity of the slurry through interaction with PVDF5130 and PVDF900, making the slurry easier to apply and disperse. This synergistic effect helps to reduce the gelation of the slurry during mixing and coating. Moreover, the present application adopts the combination of PVDF5130, PAA and PVDF900, which is conducive to improving the dispersion stability of the slurry after adding the lithium supplement, helping to reduce the separation and excessive mixing of the electrode clusters, thereby maintaining the uniformity and stability of the slurry and reducing the risk of gelation. The combination of PVDF5130, PAA and PVDF900 can also optimize the coating effect of the binder, and can be more evenly coated on the surface of the positive electrode particles. This uniform coating effect helps to reduce direct contact and agglomeration between particles, while improving the interface stability between the positive electrode material and the electrolyte.

[0025] The present application adopts the above-mentioned positive electrode lithium replenishing binder, and when used in combination with the lithium replenishing agent, by adopting a combination of PVDF5130, PAA and PVDF900, and the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6", relative to the use of any one or any two of PVDF5130, the PAA and the PVDF900 alone, by using the combination of VDF5130, PAA and PVDF900 at the same time, the gel problem of the positive electrode slurry can be significantly further solved, and the slurry agglomeration problem can also be solved, which is beneficial to improve the positive electrode electrical specific capacity and the positive electrode discharge specific capacity. The applicant has found that the positive electrode charge specific capacity can reach more than 164mAh / g, and the positive electrode discharge specific capacity can reach more than 154mAh / g.

[0026] In one embodiment, the mass ratio of the PVDF5130, the PAA and the PVDF900 is 1.4:0.2:0.4. The applicant has found that by using the above mass ratio of the PVDF5130, the PAA and the PVDF900, the positive electrode charge capacity can reach 200mAh / g, and the positive electrode discharge capacity can reach 160mAh / g.

[0027] In the second aspect, the present application also provides a positive electrode slurry, including a positive electrode main material, a lithium supplement agent, a conductive agent, a solvent, and a positive electrode lithium supplement binder as described in any of the above embodiments. For example, the positive electrode main material is lithium iron phosphate, for example, the lithium supplement agent is at least one of Li2NiO2 and Li5FeO, for example, the conductive agent is SP, for example, the solvent is NMP, for example, the mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is "86-95": "1-10": 2: "1-1.6": "0.2-0.4": "0.2-0.6". For example, the mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is 86:10:2:1.4:0.2:0.4. For example, the preparation and coating process of the positive electrode slurry is as follows: (1) prepare the PVDF5130, the PAA and the PVDF900 and mix them; (2) prepare the materials according to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA: PVDF900, place the prepared materials in a stirring tank, add NMP solvent, and finally stir and slurry on a high-speed disperser; then apply the positive electrode slurry and carry out the subsequent positive electrode sheet making process. For another example, the mass ratio of NMP solvent to the prepared materials is 666:1000.

[0028] In the third aspect, the present application also provides a positive electrode sheet, including a current collector and a positive electrode active layer located on the current collector, wherein the positive electrode active layer includes a lithium supplement and a positive electrode lithium supplement binder as described in any of the above embodiments. In one embodiment, the positive electrode active layer also includes a positive electrode main material and a conductive agent, wherein the positive electrode main material is lithium iron phosphate; and / or, the lithium supplement is at least one of Li2NiO2 and Li5FeO; and / or, the conductive agent is SP. For example, the mass ratio of the positive electrode main material, the lithium supplement, the conductive agent, the PVDF5130, the PAA and the PVDF900 is "86-95": "1-10": 2: "1-1.6": "0.2-0.4": "0.2-0.6". The positive electrode active layer of the positive electrode sheet of this embodiment adopts a combination of PVDF5130, PAA and PVDF900, and the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6". Compared with the use of any one or any two of PVDF5130, the PAA and the PVDF900 alone, by using the combination of VDF5130, PAA and PVDF900 at the same time, the gel problem of the positive electrode slurry can be significantly further solved, and the slurry agglomeration problem can also be solved, which is beneficial to improve the positive electrode electrical capacity and the positive electrode discharge capacity. The applicant has found that the positive electrode charge capacity can reach more than 164mAh / g, and the positive electrode discharge capacity can reach more than 154mAh / g.

[0029] For example, the mass ratio of the positive electrode main material, the lithium supplement, the conductive agent, the PVDF5130, the PAA and the PVDF900 is 86:10:2:1.4:0.2:0.4. The applicant has found that by using the above mass ratio of the PVDF5130, the PAA and the PVDF900, the positive electrode charge capacity can reach 200mAh / g, and the positive electrode discharge capacity can reach 160mAh / g.

[0030] In a fourth aspect, the present application also provides a lithium battery, comprising a positive electrode sheet as described in any of the above embodiments.

[0031] The present application adopts the above-mentioned positive electrode lithium replenishing binder, and when used in combination with the lithium replenishing agent, by adopting a combination of PVDF5130, PAA and PVDF900, and the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6", relative to the use of any one or any two of PVDF5130, the PAA and the PVDF900 alone, by using the combination of VDF5130, PAA and PVDF900 at the same time, the gel problem of the positive electrode slurry can be significantly further solved, and the slurry agglomeration problem can also be solved, which is beneficial to improve the positive electrode electrical specific capacity and the positive electrode discharge specific capacity. The applicant has found that the positive electrode charge specific capacity can reach more than 164mAh / g, and the positive electrode discharge specific capacity can reach more than 154mAh / g.

[0032] The present application will be further described below in conjunction with specific embodiments.

[0033] Example 1

[0034] 1. Prepare a positive electrode binder composition with a mass ratio of 70% PVDF5130 + 10% PAA + 20% PVDF900;

[0035] 2. According to the positive electrode ratio of lithium iron phosphate: lithium supplement agent: SP: PVDF5130: PAA: PVDF900 = 93: 3: 2: 1.4: 0.2: 0.4, 1 kg of the material was placed in a 5L stirring tank, 666 g of NMP solvent was added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement agent was Li2NiO2.

[0036] 3. Observe the state of the slurry and then apply it;

[0037] 4. The electrode sheet using the multi-component positive electrode binder is made into a 2.5Ah soft-pack battery, and the charge and discharge tester (5V5A) is used for charge and discharge; the charge and discharge process is: 0.1C CC to 3.65V, 0.05C CC to4.3V, CV to 0.01C, 0.1C DC to 2.0V;

[0038] Example 2

[0039] 1. Prepare a positive electrode binder composition with a mass ratio of 20% PVDF5130 + 10% PAA + 70% PVDF900;

[0040] 2. According to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA: PVDF900 = 93: 3: 2: 0.4: 0.2: 1.4, 1 kg of the material was placed in a 5L stirring tank, 666 g of NMP solvent was added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement was Li2NiO2.

[0041] 3. Observe the state of the slurry and then apply it;

[0042] Example 3

[0043] 1. Prepare a positive electrode binder composition with a mass ratio of 10% PVDF5130 + 70% PAA + 20% PVDF900;

[0044] 2. According to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA: PVDF900 = 93: 3: 2: 0.2: 1.4: 0.4, 1 kg of the material was placed in a 5L stirring tank, 666 g of NMP solvent was added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement was Li2NiO2.

[0045] 3. Observe the state of the slurry and then apply it;

[0046] Example 4

[0047] 1. Prepare a positive electrode binder composition with a mass ratio of 50% PVDF5130+20% PAA+30% PVDF900;

[0048] 2. According to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA: PVDF900 = 93: 3: 2: 1: 0.4.0: 0.6, 1 kg of the material was placed in a 5L stirring tank, 666 g of NMP solvent was added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement was Li2NiO2.

[0049] 3. Observe the state of the slurry and then apply it;

[0050] Example 5

[0051] 1. Prepare a positive electrode binder composition with a mass ratio of 80% PVDF5130 + 10% PAA + 10% PVDF900;

[0052] 2. According to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA: PVDF900 = 93: 3: 2: 1.6: 0.2: 0.2, 1 kg of the material was placed in a 5L stirring tank, 666 g of NMP solvent was added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement was Li2NiO2.

[0053] 3. Observe the state of the slurry and then apply it;

[0054] Example 6

[0055] 1. Prepare a positive electrode binder composition with a mass ratio of 70% PVDF5130 + 10% PAA + 20% PVDF900;

[0056] 2. According to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA: PVDF900 = 95: 1: 2: 1.4: 0.2: 0.4, 1 kg of the material was placed in a 5L stirring tank, 666 g of NMP solvent was added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement was Li2NiO2.

[0057] 3. Observe the state of the slurry and then apply it;

[0058] Example 7

[0059] 1. Prepare a positive electrode binder composition with a mass ratio of 70% PVDF5130 + 10% PAA + 20% PVDF900;

[0060] 2. According to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA: PVDF900 = 86:10:2:1.4:0.2:0.4, 1 kg of the material was placed in a 5L stirring tank, 666 g of NMP solvent was added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement was Li2NiO2.

[0061] 3. Observe the state of the slurry and then apply it;

[0062] Comparative Example 1

[0063] 1. According to the positive electrode ratio of lithium iron phosphate: SP: PVDF900 = 96:2:2, 1 kg of the material is placed in a 5L stirring tank, 666 g of NMP solvent is added, and finally stirred and homogenized on a high-speed disperser;

[0064] 2. Observe the state of the slurry and then apply it;

[0065] Comparative Example 2

[0066] 1. According to the positive electrode ratio of lithium iron phosphate: lithium supplement agent: SP: PVDF900 = 91:5:2:2, 1 kg of the material is placed in a 5L stirring tank, 666 g of NMP solvent is added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement agent is Li2NiO2.

[0067] 2. Observe the state of the slurry and then apply it;

[0068] Comparative Example 3

[0069] 1. According to the positive electrode ratio of lithium iron phosphate: lithium supplement agent: SP: PVDF900 = 93:3:2:2, 1 kg of the material is placed in a 5L stirring tank, 666 g of NMP solvent is added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement agent is Li2NiO2.

[0070] 2. Observe the state of the slurry and then apply it;

[0071] Comparative Example 4

[0072] 1. According to the positive electrode ratio of lithium iron phosphate: lithium supplement agent: SP: PAA = 93:3:2:2, 1 kg of the material is placed in a 5L stirring tank, 666 g of NMP solvent is added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement agent is Li2NiO2.

[0073] 2. Observe the state of the slurry and then apply it;

[0074] Comparative Example 5

[0075] 1. According to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA = 93: 3: 2: 1.6: 0.4, 1 kg of the material is placed in a 5L stirring tank, 666 g of NMP solvent is added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement is Li2NiO2.

[0076] 2. Observe the state of the slurry and then apply it;

[0077] Comparative Example 6

[0078] 1. According to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PVDF900 = 93:3:2:0.4:1.6, 1 kg of the material was placed in a 5L stirring tank, 666 g of NMP solvent was added, and finally stirred and homogenized on a high-speed disperser; the lithium supplement was Li2NiO2.

[0079] 2. Observe the state of the slurry and then apply it;

[0080] The test results are shown in Table 1.

[0081] Table 1 Proportions and test results of various embodiments and comparative examples

[0082]

[0083] As can be seen from Table 1, compared with each comparative example, each embodiment can significantly improve the slurry agglomeration and gel problems, and can significantly improve the positive electrode specific capacity and the positive electrode discharge specific capacity. The applicant has found that the positive electrode charge specific capacity can reach more than 164mAh / g, and the positive electrode discharge specific capacity can reach more than 154mAh / g. In Example 7, by mixing the ingredients according to the positive electrode ratio of lithium iron phosphate: lithium supplement: SP: PVDF5130: PAA: PVDF900 = 86: 10: 2: 1.4: 0.2: 0.4, the positive electrode charge specific capacity can reach 200mAh / g, and the positive electrode discharge specific capacity can reach 160mAh / g.

[0084] When PVDF900 is used alone in Comparative Example 1, although agglomeration and gelation can be improved to a certain extent, the positive electrode charge capacity and positive electrode discharge capacity still have room for improvement. Compared with Comparative Example 1, other embodiments have higher positive electrode charge capacity and positive electrode discharge capacity, indicating that other embodiments can further improve the agglomeration and gelation problems compared with Comparative Example 1.

[0085] like Figure 1 As shown, it is a picture of the positive electrode slurry in Comparative Example 2. The positive electrode slurry in Comparative Example 2 was stirred, and the slurry gelled obviously, had no fluidity, and could not be effectively coated on the aluminum foil. At the same time, unexpectedly, in Example 2, due to the reduction in the PVDF5130 content, there was a problem of unsuccessful coating. In Example 3, it could be coated, but the pole piece was brittle and could not be processed. Therefore, according to Example 1 and Examples 4 to 7, it can be concluded that in the ratio of each component of the positive electrode lithium supplement binder, PVDF5130, PAA and PVDF900, wherein the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6" is more suitable.

[0086] like Figures 2 to 4 , which is the photo in Example 1 of the present application, Figure 2 When the slurry flows, no slurry gel occurs. Figure 3 This is a photo of the positive electrode sheet, which can be coated on aluminum foil without particle agglomeration. Figure 3 This is a photo after folding. The electrode was folded three times without any powder falling off or breaking.

[0087] Furthermore, the electrodes prepared in Example 1 and Comparative Example 1 were respectively made into 2.5Ah soft-pack batteries, and charged and discharged using a charge and discharge tester (5V5A); the charge and discharge process was: 0.1C CC to 3.65V, CV to 0.01C, 0.1C DC to2.0V;

[0088] The charge and discharge data and curves of the test of Example 1 are as follows: Figure 5 The charging capacity of the lithium supplement agent is 400mAh / g, the charging capacity of lithium iron phosphate is 160mAh / g, the first charging capacity of the positive electrode active material is 172mAh / g, and the first discharge capacity of the positive electrode active material is 160mAh / g. The addition of the lithium supplement agent completely compensates for the lithium loss caused by the formation of SEI during the first charge and discharge of lithium iron phosphate, making the subsequent charge and discharge capacity of lithium iron phosphate close to 100%.

[0089] The charge and discharge data and curves of the test of comparative example 1 are as follows: Figure 6 The theoretical specific charging capacity of lithium iron phosphate is 160mAh / g, the actual specific charging capacity of the positive electrode active material is 160mAh / g, the first discharge capacity of the positive electrode active material is 148mAh / g, and the lithium loss forming SEI is 12mAh / g.

[0090] It can be determined that, compared with the comparative examples, Examples 1 and 4-8 of the present application can significantly improve the lithium loss caused by SEI loss.

[0091] The present application adopts the above-mentioned positive electrode lithium replenishing binder, and when used in combination with the lithium replenishing agent, by adopting a combination of PVDF5130, PAA and PVDF900, and the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6", relative to the use of any one or any two of PVDF5130, the PAA and the PVDF900 alone, by using the combination of VDF5130, PAA and PVDF900 at the same time, the gel problem of the positive electrode slurry can be significantly further solved, and the slurry agglomeration problem can also be solved, which is beneficial to improve the positive electrode electrical specific capacity and the positive electrode discharge specific capacity. The applicant has found that the positive electrode charge specific capacity can reach more than 164mAh / g, and the positive electrode discharge specific capacity can reach more than 154mAh / g.

[0092] The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. It should be noted that "in one embodiment", "for example", "for example", etc. in this application are intended to illustrate the present application, rather than to limit the present application. The above-described embodiments only express several implementation methods of the present application, and the description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the patent application. It should be pointed out that for a person of ordinary skill in the art, without departing from the concept of the present application, several variations and improvements can also be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be subject to the attached claims.

Claims

1. A positive electrode lithium supplement binder, characterized in that: It includes PVDF5130, PAA and PVDF900, wherein the mass ratio of the PVDF5130, the PAA and the PVDF900 is "1-1.6": "0.2-0.4": "0.2-0.6".

2. The positive electrode lithium supplement binder according to claim 1, characterized in that: The mass ratio of the PVDF5130, the PAA and the PVDF900 is 1.4:0.2:0.

4.

3. A positive electrode slurry, characterized in that: The invention comprises a positive electrode main material, a lithium replenishing agent, a conductive agent, a solvent and the positive electrode lithium replenishing binder as claimed in claim 1 or 2.

4. The positive electrode slurry according to claim 3, characterized in that: The positive electrode main material is lithium iron phosphate, the lithium supplement agent is at least one of Li2NiO2 and Li5FeO, the conductive agent is SP, the solvent is NMP, and the mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is "86-95":"1-10":2:"1-1.6":"0.2-0.4":"0.2-0.6".

5. The positive electrode slurry according to claim 4, characterized in that: The mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is 86:10:2:1.4:0.2:0.

4.

6. A positive electrode sheet, comprising a current collector and a positive electrode active layer located on the current collector, characterized in that: The positive electrode active layer includes a lithium replenishing agent and the positive electrode lithium replenishing binder as claimed in claim 1 or 2.

7. The positive electrode sheet according to claim 6, characterized in that: The positive electrode active layer further includes a positive electrode main material and a conductive agent, wherein the positive electrode main material is lithium iron phosphate; and / or the lithium supplement is at least one of Li2NiO2 and Li5FeO; and / or the conductive agent is SP.

8. The positive electrode sheet according to claim 7, characterized in that: The mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is "86-95":"1-10":2:"1-1.6":"0.2-0.4":"0.2-0.6".

9. The positive electrode sheet according to claim 8, characterized in that: The mass ratio of the positive electrode main material, the lithium supplement agent, the conductive agent, the PVDF5130, the PAA and the PVDF900 is 86:10:2:1.4:0.2:0.

4.

10. A lithium battery, characterized in that: Comprising the positive electrode sheet as described in any one of claims 6 to 9.

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