Modified polyurethane, method for preparing the same, negative electrode sheet, secondary battery, and electric device

Abstract

This application provides a modified polyurethane and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device, belonging to the field of secondary battery technology. The modified polyurethane contains C-F bonds and / or -COO bonds. ‑ Li + The modified polyurethane can effectively improve the cycle performance and first-cycle efficiency of the battery, and reduce the amount of gas generated during battery formation.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, specifically relating to modified polyurethane and its preparation method, negative electrode sheet, secondary battery and power device. Background Technology

[0002] Lithium-ion batteries have developed rapidly due to their outstanding advantages such as long cycle life, high energy density, and environmental friendliness, and are widely used in portable electronic products, energy storage devices, new energy vehicles and other fields.

[0003] Silicon-based materials have high energy density and are considered key anode materials for next-generation high-energy-density lithium-ion batteries. However, silicon-based materials undergo significant volume changes during charge and discharge, leading to rapid capacity decay and a substantial reduction in cycle life. Currently, a PAA+SBR+CMC adhesive system is commonly used to enhance the binding of silicon-based materials and improve battery cycle performance, but this effect is not significant. Furthermore, it cannot alleviate the problem of poor conductivity of the anode electrode, resulting in low initial efficiency during capacity grading, or the problem of the anode electrode easily reacting with the electrolyte, leading to high gas production during battery formation.

[0004] Patent application CN 110247023 A discloses a novel method for reinforcing battery electrodes and a corresponding electrode. The reinforcement method includes the following steps: S1: dissolving an aqueous binder in water to obtain a binder solution; S2: preparing a polyurethane solution.

[0005] S3: Mix the binder solution obtained in step S1 with conductive carbon black and the source material corresponding to the alloy-type negative electrode material, and grind them into a slurry; S4: Coat the slurry obtained in step S3 evenly onto the surface of copper foil, and then dry it to obtain an electrode sheet; S5: ...

[0006] The electrode obtained in step S4 is immersed in the polyurethane solution obtained in step S2, then removed and dried to obtain an enhanced battery electrode. Compared to existing single binder systems, this polyurethane composite binder has both adhesive and elastic properties, effectively mitigating the volume expansion of silicon during charging and discharging, and improving the cycle performance of silicon as a lithium battery anode material. Furthermore, the aqueous binder forms an aqueous binder solution, and the polyurethane forms an organic polyurethane solution. After coating the slurry containing the binder solution onto the surface of the anode material current collector and drying it, the electrode is then immersed in the polyurethane solution. This utilizes the advantage of the immiscibility between the aqueous and organic phases. Crucially, further composite of the electrode with the polyurethane binder reduces porosity, thereby decreasing the contact area between the electrode material and the electrolyte, effectively improving the battery's initial coulombic efficiency. Summary of the Invention

[0007] This application is based on the inventor's discovery and understanding of the following facts and problems: the battery cycle performance and first-efficiency rating of the battery in patent application CN110247023A still need to be improved; in addition, the amount of gas generated during battery formation still needs to be reduced.

[0008] This application aims to at least partially address one of the technical problems in related technologies. To this end, embodiments of this application propose a modified polyurethane and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device. Compared to polyurethane binders in related technologies, this modified polyurethane can improve the battery's cycle performance and first-cycle efficiency, while reducing the amount of gas generated during battery formation.

[0009] The first aspect of this application provides a modified polyurethane, wherein the modified polyurethane contains CF bonds and / or -COO bonds. - Li + Polyurethane.

[0010] In some embodiments, when the modified polyurethane is a polyurethane containing CF bonds, the structure of the modified polyurethane is as shown in the following formula:

[0011]

[0012] Where n = 2 to 56;

[0013] When the modified polyurethane contains -COO - Li + When using polyurethane, the structure of the modified polyurethane is shown in the following formula:

[0014]

[0015] Where n = 2 to 56;

[0016] When the modified polyurethane contains CF bonds and -COO - Li + When using polyurethane, the structure of the modified polyurethane is shown in the following formula:

[0017]

[0018] Where n = 2 to 56.

[0019] In some embodiments, the content of F element is 2 wt.% to 7 wt.% based on 100 wt.% of the total mass of the modified polyurethane; and / or, the content of Li element is 1.2 wt.% to 4 wt.% based on 100 wt.% of the total mass of the modified polyurethane.

[0020] The second aspect of this application provides a method for preparing a modified polyurethane, used to prepare the modified polyurethane of the first aspect.

[0021] When the modified polyurethane is a polyurethane containing CF bonds, the preparation method includes the following steps:

[0022] S1-1. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer;

[0023] S2-1. The first prepolymer, chain extender, fluorinated butanediol and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer;

[0024] S3-1. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; the solvent in the emulsion is removed by distillation to obtain the modified polyurethane;

[0025] When the modified polyurethane is a polyurethane containing lithium functional groups, the preparation method includes the following steps:

[0026] S1-2. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer;

[0027] S2-2. The first prepolymer, chain extender and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer;

[0028] S3-2. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; then LiOH is added dropwise to the emulsion until the pH of the emulsion is neutral, and then the solvent in the emulsion is removed by distillation to obtain the modified polyurethane;

[0029] When the modified polyurethane is a polyurethane containing CF bonds and lithium functional groups, the preparation method includes the following steps:

[0030] S1-3. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer;

[0031] S2-3. The first prepolymer, chain extender, fluorinated butanediol and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer;

[0032] S3-3. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; then LiOH is added dropwise to the emulsion until the pH of the emulsion is neutral, and then the solvent in the emulsion is removed by distillation to obtain the modified polyurethane.

[0033] In some embodiments, the polymerization reaction is carried out at a temperature of 80–100°C for 2–5 hours; and / or the chain extension reaction is carried out at a temperature of 60–90°C for 4–6 hours.

[0034] A third aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer comprising a negative electrode active material, a binder and optionally a conductive agent, the negative electrode active material comprising a silicon-based material, and the binder comprising a modified polyurethane of the first aspect.

[0035] In some embodiments, the content of F element in the negative electrode film is 0.10 g / m³. 2 ~0.16g / m 2 .

[0036] In some embodiments, the Li content in the negative electrode film is 0.008 g / m³. 2 ~0.013g / m 2 .

[0037] In some embodiments, the content of the silicon-based material is 3 wt.% to 15 wt.% based on a total mass of 100 wt.% of the negative electrode film.

[0038] In some embodiments, the content of the conductive agent is 0.5 wt.% to 1.5 wt.%.

[0039] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, a first binder, and optionally a first conductive agent. The second negative electrode film layer includes a second negative electrode active material, a second binder, and optionally a second conductive agent. The first negative electrode active material includes a first silicon-based material, and / or the first binder includes a first modified polyurethane, and / or the second negative electrode active material includes a second silicon-based material, and / or the second binder includes a second modified polyurethane.

[0040] In some embodiments, the content of F element in the first negative electrode film layer is 0.02 g / m 2 ~0.06g / m 2 ; and / or, the F element content in the second negative electrode film is 0.05 g / m 2 ~0.12g / m 2 ; and / or, the ratio of the F element content in the second negative electrode film to the F element content in the first negative electrode film is 1 to 5.

[0041] In some embodiments, the Li content in the first negative electrode film is 0.004 g / m³. 2 ~0.011g / m 2 ; and / or, the Li content in the second negative electrode film is 0.002 g / m 2 ~0.005g / m 2 ; and / or, the ratio of the Li element content in the second negative electrode film to the Li element content in the first negative electrode film is 0.18 to 0.90.

[0042] In some embodiments, based on a total mass of 100 wt.% of the first negative electrode film, the content of the first silicon-based material in the first negative electrode film is 3 wt.% to 8 wt.%; and / or, based on a total mass of 100 wt.% of the second negative electrode film, the content of the second silicon-based material in the second negative electrode film is 4 wt.% to 16 wt.%; and / or, the ratio of the content of the second silicon-based material in the second negative electrode film to the content of the first silicon-based material in the first negative electrode film is 1 to 3.

[0043] In some embodiments, based on a total mass of 100 wt.% of the first negative electrode film, the content of the first conductive agent in the first negative electrode film is 0.9 wt.% to 1.1 wt.%, for example, 0.9 wt.%, 0.92 wt.%, 0.94 wt.%, 0.96 wt.%, 0.98 wt.%, 1.0 wt.%, 1.02 wt.%, 1.04 wt.%, 1.06 wt.%, 1.08 wt.%, 1.1 wt.%, etc.

[0044] In some embodiments, based on a total mass of 100 wt.% of the first negative electrode film, the content of the first conductive agent in the first negative electrode film is 0.9 wt.% to 1.1 wt.%; and / or, based on a total mass of 100 wt.% of the second negative electrode film, the content of the second conductive agent in the second negative electrode film is 1.0 wt.% to 1.5 wt.%; and / or, the ratio of the content of the second conductive agent in the second negative electrode film to the content of the first conductive agent in the first negative electrode film is 1.05 to 1.5.

[0045] The fourth aspect of this application provides a secondary battery, which includes the negative electrode sheet of the third aspect.

[0046] The fifth aspect of this application provides an electrical device, which includes a secondary battery as described in the fourth aspect.

[0047] Compared with related technologies, the advantages and technical effects of the embodiments of this application are as follows:

[0048] (1) The modified polyurethane in this application embodiment contains CF bonds and / or lithium functional groups. The CF bonds are highly polar and are not easily broken after film formation, which is beneficial to the maintenance of adhesion during the rolling process. The lithium functional groups can improve the adhesion between the negative electrode film layer and the negative electrode current collector and the cohesion of the negative electrode film layer, and enhance the binding of the negative electrode material. Therefore, compared with the polyurethane adhesive in the related technology, the polyurethane adhesive in this application embodiment can improve the adhesion between the negative electrode film layer and the negative electrode current collector and the cohesion of the negative electrode film layer.

[0049] (2) The modified polyurethane in this application embodiment enhances the adhesion between the negative electrode film and the negative electrode current collector and the cohesion of the negative electrode film, reduces the pulverization of the negative electrode material during cycling, and effectively improves the cycle performance of the battery.

[0050] (3) The modified polyurethane improves the adhesion between the negative electrode film and the negative electrode current collector, which reduces the expansion and cracking of the negative electrode particles during the first charge and discharge process, thus reducing the loss of active lithium and improving the first-time efficiency of the battery. In addition, the modified polyurethane in this embodiment contains lithium-ion functional groups, which can improve the conductivity of the negative electrode film and reduce the internal resistance of the negative electrode film, thereby improving the first-time efficiency of the battery. Furthermore, the lithium-ion functional groups also have the effect of additional lithium replenishment during the first charge and discharge, which also helps to improve the first-time efficiency of the battery.

[0051] (4) The modified polyurethane in this application contains CF bonds, which can effectively reduce the affinity of the negative electrode film for water and reduce the adsorption of water, thereby reducing the side reaction between the negative electrode film and the electrolyte and reducing the amount of gas generated during battery formation.

[0052] (5) The preparation method of the modified polyurethane in the second aspect of the present application is simple to operate and easy to promote industrially.

[0053] (6) Due to the use of the modified polyurethane of the first aspect of the present application, the negative electrode sheet of the third aspect of the present application has strong adhesion between the negative electrode film layer and the negative electrode current collector, high cohesion of the negative electrode film layer, good conductivity and low internal resistance.

[0054] (7) Because the negative electrode sheet of the third aspect of the present application is adopted, the secondary battery of the fourth aspect of the present application and the power supply device of the fifth aspect have good cycle performance, high first efficiency and low formation gas production. Detailed Implementation

[0055] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0057] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0058] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0059] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0060] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0061] The first aspect of this application provides a modified polyurethane, wherein the modified polyurethane contains CF bonds and / or -COO bonds. - Li + Polyurethane.

[0062] The modified polyurethane in this application contains CF bonds and / or lithium-ion functional groups -COO. - Li + The polyurethane has strong CF bonds, which are not easily broken after film formation, thus helping to maintain adhesion during rolling. The lithium-ion functional group -COO... - Li + It can improve the adhesion between the negative electrode film layer and the negative electrode current collector and the cohesion of the negative electrode film layer, and enhance the binding of the negative electrode material. Therefore, compared with the polyurethane adhesive in the related technology, the polyurethane adhesive of this application embodiment can improve the adhesion between the negative electrode film layer and the negative electrode current collector and the cohesion of the negative electrode film layer.

[0063] The modified polyurethane in this application embodiment enhances the adhesion between the negative electrode film and the negative electrode current collector, as well as the cohesive force of the negative electrode film, reducing pulverization of the negative electrode material during cycling and effectively improving the cycle performance of the battery.

[0064] The modified polyurethane improves the adhesion between the negative electrode film and the negative electrode current collector, reducing the expansion and cracking of negative electrode particles during the first charge and discharge process. This results in less loss of active lithium and improves the battery's initial efficiency during capacity grading. Furthermore, the modified polyurethane in this embodiment contains the lithium-ion functional group -COO. - Li + It can improve the conductivity of the negative electrode film, reduce the internal resistance of the negative electrode film, and improve the first-stage efficiency of the battery during capacity grading; in addition, the lithium-ion functional group -COO - Li + It also provides additional lithium replenishment during the first charge and discharge cycle, and helps improve the initial efficiency of battery capacity grading.

[0065] The modified polyurethane in this application contains CF bonds, which can effectively reduce the affinity of the negative electrode film for water, reduce water adsorption, thereby reducing the side reactions between the negative electrode film and the electrolyte, and reducing the amount of gas generated during battery formation.

[0066] In some embodiments, when the modified polyurethane is a polyurethane containing CF bonds, the structure of the modified polyurethane is as shown in the following formula:

[0067]

[0068] Where n = 2 to 56.

[0069] In some embodiments, when the modified polyurethane contains -COO - Li + When using polyurethane, the structure of the modified polyurethane is shown in the following formula:

[0070]

[0071] Where n = 2 to 56.

[0072] In some embodiments, when the modified polyurethane contains CF bonds and -COO - Li + When using polyurethane, the structure of the modified polyurethane is shown in the following formula:

[0073]

[0074] Where n = 2 to 56.

[0075] Lithyl group - COO - Li +It has hydrophilicity, strong polarity of CF bond and slightly hydrophobicity. These two functional groups are set at both ends of the polyurethane molecular chain, which can reduce the polymerization difficulty of modified polyurethane and reduce the mutual influence between the two functional groups, and avoid the strong polarity of CF bond affecting the lithium functional group.

[0076] In some embodiments, based on 100 wt.% of the total mass of the modified polyurethane, the content of element F is 2 wt.% to 7 wt.%, for example, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, 5 wt.%, 5.5 wt.%, 6 wt.%, 6.5 wt.%, 7 wt.%, etc. Element F is beneficial for film formation, reduces the water content in the electrode, does not deteriorate adhesion, has good resistance to electrolyte, can reduce the swelling and failure of the modified polyurethane adhesive, and reduces the amount of gas generated during battery formation. When the content of element F in the modified polyurethane is too low, the content of element F in the negative electrode film may be too low, which is not conducive to reducing the amount of gas generated during battery formation. However, when the content of element F in the modified polyurethane is too high, the content of element F in the negative electrode film may be too high, which is not conducive to improving the conductivity of the negative electrode film.

[0077] In some embodiments, based on 100 wt.% of the total mass of the modified polyurethane, the Li element content is 1.2 wt.% to 4 wt.%, for example, 1.2 wt.%, 1.4 wt.%, 1.6 wt.%, 1.8 wt.%, 2 wt.%, 2.2 wt.%, 2.4 wt.%, 2.6 wt.%, 2.8 wt.%, 3 wt.%, 3.2 wt.%, 3.4 wt.%, 3.6 wt.%, 3.8 wt.%, 4 wt.%, etc. Lithium-containing functional group - COO - Li + Good conductivity can improve the conductivity of the negative electrode film, reduce its internal resistance, and improve the battery's initial efficiency during capacity testing. However, if the Li content in the modified polyurethane is too low, the Li content in the negative electrode film may also be too low, which is detrimental to reducing the internal resistance of the negative electrode film and thus hinders the improvement of the battery's initial efficiency during capacity testing. Conversely, if the Li content in the modified polyurethane is too high, the Li content in the negative electrode film may also be too high, making the negative electrode film prone to water absorption and hindering the improvement of adhesion between the film and the negative electrode current collector.

[0078] The second aspect of this application provides a method for preparing a modified polyurethane, used to prepare the modified polyurethane of the first aspect. The preparation methods for different types of modified polyurethane in the first aspect will be described below.

[0079] When the modified polyurethane is a polyurethane containing CF bonds, the preparation method includes the following steps:

[0080] S1-1. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer;

[0081] S2-1. The first prepolymer, chain extender, fluorinated butanediol and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer;

[0082] S3-1. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; the solvent in the emulsion is removed by distillation to obtain the modified polyurethane.

[0083] Step S1-1 is used to prepare polyurethane, the fluorinated butanediol in step S2-1 can provide CF functional group modification for polyurethane, and step S3-1 can obtain a stable modified polyurethane.

[0084] When the modified polyurethane is a lithium-functionalized COO - Li + When preparing polyurethane, the preparation method includes the following steps:

[0085] S1-2. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer;

[0086] S2-2. The first prepolymer, chain extender and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer;

[0087] S3-2. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; then LiOH is added dropwise to the emulsion until the pH of the emulsion is neutral, and then the solvent in the emulsion is removed by distillation to obtain the modified polyurethane.

[0088] Steps S1-2 and S2-2 are used to prepare polyurethane, while step S3-2 provides lithium-ion functional groups to the polyurethane and also makes the modified polyurethane stable.

[0089] When the modified polyurethane contains CF bonds and lithium functional groups -COO - Li + When preparing polyurethane, the preparation method includes the following steps:

[0090] S1-3. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer;

[0091] S2-3. The first prepolymer, chain extender, fluorinated butanediol and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer;

[0092] S3-3. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; then LiOH is added dropwise to the emulsion until the pH of the emulsion is neutral, and then the solvent in the emulsion is removed by distillation to obtain the modified polyurethane.

[0093] Steps S1-3 are used to prepare polyurethane. The fluorinated butanediol in steps S2-3 can provide CF functional group modification for polyurethane. Step S3-3 provides lithium functional group modification for polyurethane on the one hand, and can make the modified polyurethane stable on the other hand.

[0094] In some embodiments, the polymerization reaction temperature is 80–100°C, such as 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C, 100°C, etc.; the polymerization reaction time is 2–5 hours, such as 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc. When the polymerization reaction temperature is too low or the time is too short, the reaction is difficult to occur or the reaction is slow, resulting in a small amount of prepolymer generated. When the polymerization reaction temperature is too high or the time is too long, it is not conducive to cost reduction and efficiency improvement.

[0095] In some embodiments, the chain extension reaction temperature is 60–90°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.; the chain extension reaction time is 4–6 hours, such as 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, etc. When the chain extension reaction temperature is too low or the time is too short, it is not conducive to the polymerization of modified functional groups with the prepolymer, and it is not conducive to improving the uniformity of the distribution of modified functional groups on the polyurethane molecular chain. When the chain extension reaction temperature is too high or the time is too long, it is not conducive to cost reduction and efficiency improvement.

[0096] A third aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer comprising a negative electrode active material, a binder and optionally a conductive agent, the negative electrode active material comprising a silicon-based material, and the binder comprising a modified polyurethane of the first aspect.

[0097] Because the modified polyurethane of the first aspect of the present application is used, the negative electrode sheet of the third aspect of the present application has strong adhesion between the negative electrode film layer and the negative electrode current collector, high cohesion of the negative electrode film layer, good conductivity and low internal resistance.

[0098] In the negative electrode sheet of this application embodiment, the modified polyurethane used in the negative electrode film layer can be a polyurethane containing CF bonds, or it can be a polyurethane containing -COO bonds. - Li + Polyurethane can also contain CF bonds and -COO bonds. - Li+ Polyurethane, or polyurethane containing CF bonds combined with polyurethane containing -COO bonds. - Li + Polyurethane compound is used.

[0099] In some embodiments, the content of F element in the negative electrode film is 0.035 g / m³. 2 ~0.16g / m 2 .

[0100] In some embodiments, the content of F element in the negative electrode film is 0.10 g / m³. 2 ~0.16g / m 2 For example, 0.10g / m 2 0.105g / m 2 0.11g / m 2 0.11g / m 2 0.12g / m 2 0.125g / m 2 0.13g / m 2 0.135g / m 2 0.14g / m 2 0.145g / m 2 0.15g / m 2 0.155g / m 2 0.16g / m 2 F (fluorine) is beneficial for film formation, reduces water content in the electrode, does not worsen adhesion, has good electrolyte tolerance, and can reduce swelling and failure of modified polyurethane adhesives, thus lowering the amount of gas generated during battery formation. However, if the F content in the negative electrode film is too low, it is not conducive to reducing the amount of gas generated during battery formation. Conversely, if the F content in the negative electrode film is too high, it is not conducive to improving the conductivity of the negative electrode film.

[0101] In some embodiments, the Li content in the negative electrode film is 0.007 g / m³. 2 ~0.013g / m 2 In some embodiments, the Li content in the negative electrode film is 0.008 g / m³. 2 ~0.013g / m 2 For example, 0.008g / m 2 0.0085g / m 2 0.009g / m 2 0.0095g / m 2 0.010g / m 2 0.0105g / m 2 0.011g / m 2 0.0115g / m2 0.012g / m 2 0.0125g / m 2 0.013g / m 2 Etc. Lithylated functional group - COO - Li + Good Li content can improve the conductivity of the negative electrode film, reduce its internal resistance, and thus improve the battery's initial efficiency during capacity testing. However, if the Li content in the negative electrode film is too low, it will not be conducive to reducing the internal resistance of the negative electrode film, thereby hindering the improvement of the battery's initial efficiency during capacity testing. Conversely, if the Li content in the negative electrode film is too high, the negative electrode film will easily absorb water, which will not be conducive to improving the adhesion between the negative electrode film and the negative current collector.

[0102] In some embodiments, the adhesive content is 2.5 wt.% to 4.5 wt.%, for example, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, etc., based on the total mass of the negative electrode film layer of 100 wt.%.

[0103] In some embodiments, based on 100 wt.% of the total mass of the negative electrode film, the content of the silicon-based material is 3 wt.% to 15 wt.%, for example, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, etc. When the content of the silicon-based material in the negative electrode film is too low, it is not conducive to improving the battery capacity. When the content of the silicon-based material in the negative electrode film is too high, it is not conducive to improving the cycle performance of the battery. Preferably, based on 100 wt.% of the total mass of the negative electrode film, the content of the silicon-based material is 3 wt.% to 6 wt.%.

[0104] In some embodiments, the total mass of the negative electrode film is 100 wt.%, and the content of the negative electrode active material is 79 wt.% to 97 wt.%, for example, 79 wt.%, 80 wt.%, 90 wt.%, 91 wt.%, 92 wt.%, 93 wt.%, 94 wt.%, 95 wt.%, 96 wt.%, 97 wt.%, etc.

[0105] In some embodiments, based on a total mass of 100 wt.% of the negative electrode film, the content of the conductive agent is 0.5 wt.% to 1.5 wt.%, for example, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, etc. When the content of the conductive agent in the negative electrode film is too low, it is not conducive to improving the conductivity of the negative electrode film. When the content of the conductive agent in the negative electrode film is too high, the content of the negative electrode active material in the negative electrode film may be too low, which is not conducive to improving the battery capacity.

[0106] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, a first binder, and optionally a first conductive agent. The second negative electrode film layer includes a second negative electrode active material, a second binder, and optionally a second conductive agent. The first negative electrode active material includes a first silicon-based material, and / or the first binder includes a first modified polyurethane, and / or the second negative electrode active material includes a second silicon-based material, and / or the second binder includes a second modified polyurethane.

[0107] In the negative electrode sheet of this application embodiment, the negative electrode film layer can be a single-layer design, a double-layer design, or even a multi-layer design. If it is a double-layer or multi-layer design, at least one layer of the negative electrode film layer can be made of modified polyurethane.

[0108] In the bilayer negative electrode film, the first and second modified polyurethanes used can be the same or different. For example, both the first and second modified polyurethanes can contain CF bonds and -COO bonds. - Li + The first modified polyurethane is a polyurethane containing CF bonds and -COO bonds; or, the first modified polyurethane is a polyurethane containing CF bonds and -COO bonds. - Li + The polyurethane, the second modified polyurethane is containing -COO - Li + The first modified polyurethane is a polyurethane containing CF bonds, and the second modified polyurethane is a polyurethane containing -COO bonds. - Li + Polyurethane, etc.

[0109] In some embodiments, the content of F element in the first negative electrode film layer is 0.02 g / m 2 ~0.06g / m 2 For example, 0.02g / m 2 0.025g / m 2 0.03g / m 20.035g / m 2 0.04g / m 2 0.045g / m 2 0.05g / m 2 0.055g / m 2 0.06g / m 2 When the fluorine (F) content in the first negative electrode film is too low, it is not conducive to reducing the amount of gas generated during battery formation. When the fluorine (F) content in the first negative electrode film is too high, it is not conducive to improving the conductivity of the negative electrode film.

[0110] In some embodiments, the content of F element in the second negative electrode film is 0.05 g / m 2 ~0.12g / m 2 For example, 0.05g / m 2 0.06g / m 2 0.07g / m 2 0.08g / m 2 0.09g / m 2 0.10g / m 2 0.11g / m 2 0.12g / m 2 When the fluorine (F) content in the second negative electrode film is too low, it is not conducive to reducing the amount of gas generated during battery formation. When the fluorine (F) content in the second negative electrode film is too high, it is not conducive to improving the conductivity of the negative electrode film.

[0111] In some embodiments, the ratio of the content of F element in the second negative electrode film layer to the content of F element in the first negative electrode film layer (hereinafter referred to as the F ratio) is 1 to 5, for example, 1, 2, 3, 4, 5.

[0112] In some embodiments, the ratio of the F element content in the second negative electrode film to the F element content in the first negative electrode film (hereinafter referred to as the F ratio) is greater than 1 and less than or equal to 5. When the total F content in the negative electrode film is constant, compared to a single-layer negative electrode film, a double-layer negative electrode film with a higher F content in the second negative electrode film than in the first negative electrode film results in a higher surface F content. Therefore, the double-layer negative electrode film has a lower affinity for water, less water adsorption, and fewer side reactions with the electrolyte, leading to lower gas production during battery formation. However, when the F ratio is too high, it is detrimental to improving the adhesion between the double-layer negative electrode film and the negative electrode current collector.

[0113] In some embodiments, the Li content in the first negative electrode film is 0.004 g / m³. 2 ~0.011g / m 2 For example, 0.004 g / m 20.005g / m 2 0.006g / m 2 0.007g / m 2 0.008g / m 2 0.009g / m 2 0.010g / m 2 0.011g / m 2 When the Li content in the first negative electrode film is too low, it is not conducive to reducing the internal resistance of the negative electrode film, thus hindering the improvement of the battery's initial efficiency during capacity grading. When the Li content in the first negative electrode film is too high, the negative electrode film is prone to absorbing water, which is not conducive to improving the adhesion between the negative electrode film and the negative electrode current collector.

[0114] In some embodiments, the Li content in the second negative electrode film is 0.002 g / m³. 2 ~0.005g / m 2 For example, 0.002 g / m 2 0.0022g / m 2 0.0024g / m 2 0.0026g / m 2 0.0028g / m 2 0.003g / m 2 0.0032g / m 2 0.0034g / m 2 0.0036g / m 2 0.0038g / m 2 0.004g / m 2 0.0042g / m 2 0.0044g / m 2 0.0046g / m 2 0.005g / m 2 When the Li content in the second negative electrode film is too low, it is not conducive to reducing the internal resistance of the negative electrode film, thus hindering the improvement of the battery's initial efficiency during capacity grading. When the Li content in the second negative electrode film is too high, the negative electrode film is prone to absorbing water, which is not conducive to improving the adhesion between the negative electrode film and the negative electrode current collector.

[0115] In some embodiments, the ratio of the Li content in the second negative electrode film to the Li content in the first negative electrode film (hereinafter referred to as the Li ratio) is 0.18 to 0.90. With a fixed total Li content in the negative electrode film, compared to a single-layer negative electrode film, adjusting the Li content in the second negative electrode film to be lower than the Li content in the first negative electrode film in a double-layer negative electrode film design can more effectively balance the conductivity of the negative electrode film and reduce its internal resistance.

[0116] In the negative electrode sheet of this application embodiment, the negative electrode film layer can be a single-layer design, a double-layer design, or even a multi-layer design. If it is a double-layer or multi-layer design, at least one layer of the negative electrode film layer can have a silicon-based material.

[0117] In the double-layer negative electrode film, the first silicon-based material and the second silicon-based material used can be the same or different. That is, the first silicon-based material and the second silicon-based material can be independently selected from at least one of elemental silicon, silicon oxide (e.g., silicon suboxide), silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0118] In some embodiments, based on a total mass of 100 wt.% of the first negative electrode film, the content of the first silicon-based material in the first negative electrode film is 3 wt.% to 8 wt.%, for example, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, etc. When the content of the first silicon-based material in the first negative electrode film is too low, it is not conducive to improving the battery capacity. When the content of the first silicon-based material in the first negative electrode film is too high, it is not conducive to improving the cycle performance of the battery.

[0119] In some embodiments, based on a total mass of 100 wt.% of the second negative electrode film, the content of the second silicon-based material in the second negative electrode film is 4 wt.% to 16 wt.%, for example, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, etc. When the content of the second silicon-based material in the second negative electrode film is too low, it is not conducive to improving the battery capacity. When the content of the second silicon-based material in the second negative electrode film is too high, it is not conducive to improving the cycle performance of the battery.

[0120] In some embodiments, the ratio of the content of the second silicon-based material in the second negative electrode film to the content of the first silicon-based material in the first negative electrode film is 1 to 3, such as 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, etc.

[0121] In some embodiments, the ratio of the content of the second silicon-based material in the second negative electrode film to the content of the first silicon-based material in the first negative electrode film (hereinafter referred to as the silicon-based material ratio) is greater than 1 and less than or equal to 3. When the total silicon-based material content in the negative electrode film is constant, compared to a single-layer negative electrode film, adjusting the silicon-based material content in the second negative electrode film to be higher than that in the first negative electrode film in a double-layer negative electrode film design can enhance the active capacity of the second negative electrode film and help improve the energy density of the negative electrode sheet. However, when the silicon-based material ratio is too high, the volume expansion of the second negative electrode sheet during charging and discharging is excessive, increasing the risk of detachment and also hindering the negative electrode sheet from maintaining good conductivity.

[0122] In some embodiments, based on a total mass of 100 wt.% of the second negative electrode film, the content of the second conductive agent in the second negative electrode film is 1.0 wt.% to 1.5 wt.%, for example, 1.0 wt.%, 1.05 wt.%, 1.1 wt.%, 1.15 wt.%, 1.2 wt.%, 1.25 wt.%, 1.3 wt.%, 1.35 wt.%, 1.4 wt.%, 1.45 wt.%, 1.5 wt.%, etc.

[0123] In some embodiments, the ratio of the content of the second conductive agent in the second negative electrode film to the content of the first conductive agent in the first negative electrode film (hereinafter referred to as the conductive agent ratio) is 1.05 to 1.5, such as 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc.

[0124] The content and ratio of the first and second conductive agents are designed based on the first silicon-based material, the second silicon-based material, and the silicon-based material ratio. When the content of silicon-based material in a certain negative electrode film layer is low, the content of conductive agent in that layer can also be low. Conversely, when the content of silicon-based material in a certain negative electrode film layer is high, the content of conductive agent in that layer also needs to be high. This design approach can improve the conductivity of the negative electrode film layer.

[0125] The fourth aspect of this application provides a secondary battery, which includes the negative electrode sheet of the third aspect.

[0126] Other aspects of the secondary battery in the embodiments of this application will be described below.

[0127] [Positive electrode plate]

[0128] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0129] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0130] The positive electrode film layer includes a positive electrode active material. The positive electrode active material can be selected from materials capable of absorbing and releasing lithium.

[0131] The specific type of the positive electrode active material is not specifically limited and can be selected according to requirements. As an example, the positive electrode active material can include, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (Li2FeP2O7), lithium cobalt oxide (LiCoO2), spinel lithium manganese oxide (LiMn2O4), spinel lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), layered lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), lithium niobate (LiNbO2), lithium ferrite (LiFeO2), lithium manganate (LiMgO2), lithium calcium oxide (LiCaO2), lithium copper oxide (LiCuO2), lithium zinc oxide (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide (LiNi x Co y Al 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 0.8 Co 0.15 Al 0.05 O2), lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.), lithium-rich materials (such as lithium-rich nickel cobalt manganese oxide), manganese dioxide (MnO2), vanadium oxides, sulfur oxides, silicate oxides, and at least one of their respective modified compounds. These materials can be used alone or in combination of two or more.

[0132] The modified compounds of the above-mentioned positive electrode active materials can be modified by doping, surface coating, or both doping and coating.

[0133] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, and the modified polyurethane of the first aspect of the present application.

[0135] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0136] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0137] [Negative electrode plate]

[0138] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, a binder, and an optional conductive agent. The negative electrode active material includes a silicon-based material, and the binder includes a modified polyurethane according to the first aspect of the present application.

[0139] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0140] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0141] In some embodiments, the negative electrode active material may further include negative electrode active materials known in the art for use in batteries. As an example, the negative electrode active material may also include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0142] A composite of silicon carbide and artificial graphite is preferably used as the negative electrode active material. The artificial graphite is preferably made from needle coke and can include primary and secondary particles. The particle size Dn50 of the artificial graphite can be 9μm to 16μm, and BET can be 1.0m. 2 / g~1.6m 2 / g. The particle size of silicon carbide, Dn50, can range from 4μm to 11μm, and BET can be 1.6m. 2 / g~2.5m 2 / g, wherein the preferred silicon-carbon composition is silicon-carbon with a silicon:carbon mass ratio of approximately 55%.

[0143] In some embodiments, the adhesive may further include adhesives known in the art for use in batteries. As an example, the adhesive may also include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0144] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0145] The conductive agent can be one or more of the following: particulate spherical conductive agents (e.g., acetylene black), linear one-dimensional conductive agents (e.g., carbon nanofibers), sheet-like two-dimensional conductive agents (graphene), and tubular conductive agents (e.g., single-walled carbon nanotubes); preferably, a combination of two shapes of conductive agents. More preferably, a combination of tubular conductive agents and spherical conductive agents.

[0146] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0147] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector to form a negative electrode film layer; and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0148] In some embodiments, the negative electrode film layer is preferably double-sided coated. When the negative electrode film layer is a double-layer design, the areal density of the double-sided coating of the first negative electrode film layer is 65 g / m³. 2 ~135g / m 2 The preferred value is 100g / m 2 The surface density of the double-sided coating of the second negative electrode film is 65 g / m³. 2 ~135g / m 2 The preferred value is 100g / m 2 .

[0149] In some embodiments, the roll density of the negative electrode sheet is 1.55 to 1.75, preferably 1.65.

[0150] [Electrolytes]

[0151] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0152] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0153] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0154] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0155] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0156] [Isolation membrane]

[0157] In some embodiments, the secondary battery further includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0158] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0159] Because the modified polyurethane of the first aspect of the present application is used, the negative electrode sheet of the third aspect of the present application and the secondary battery of the fourth aspect have good cycle performance, high first efficiency and low formation gas production, and the power device of the fifth aspect can operate stably for a long time.

[0160] The fifth aspect of this application provides an electrical device, which includes a secondary battery as described in the fourth aspect.

[0161] Because the secondary battery of the fourth aspect of this application is used, the secondary battery of the fourth aspect of this application has good cycle performance, high first efficiency and low formation gas production.

[0162] This application is described in detail below with reference to embodiments.

[0163]

[0164] Example A

[0165] Under a nitrogen atmosphere, 177g of dry PPG (Mn=2000) and 50g of IPDI were added to a three-necked flask equipped with a thermometer, reflux condenser, and stir bar. The reaction was carried out at 90℃ for 3 hours. Then, 12g of DMPA and 7g of 2,2,3,3-tetrafluoro-1,4-butanediol were added, along with an appropriate amount of acetone to adjust the viscosity of the system to 3000 mPa·s. The reaction was carried out at 70℃ for 5 hours. After the reaction was completed, water was added for emulsification under high-speed stirring. LiOH solution was then added dropwise to neutralize the emulsion to pH=7. The acetone in the emulsion was then removed by vacuum distillation to obtain modified polyurethane slurry A. Modified polyurethane slurry C had a solid content of 30 wt.%, an F content of 1.3 wt.%, and a Li content of 0.25 wt.%.

[0166] Example B

[0167] Under a nitrogen atmosphere, 177g of dry PPG (Mn=2000) and 50g of IPDI were added to a three-necked flask equipped with a thermometer, reflux condenser, and stir bar. The reaction was carried out at 90℃ for 3 hours. Then, 5g of DMPA and 15g of 2,2,3,3-tetrafluoro-1,4-butanediol were added, along with an appropriate amount of acetone to adjust the viscosity of the system to 3000 mPa·s. The reaction was carried out at 70℃ for 5 hours. After the reaction was completed, water was added for emulsification under high-speed stirring. LiOH solution was then added dropwise to neutralize the emulsion to pH=7. The acetone in the emulsion was then removed by vacuum distillation to obtain modified polyurethane slurry B. Modified polyurethane slurry C had a solid content of 30 wt.%, an F content of 2.8 wt.%, and a Li content of 0.1 wt.%.

[0168] Example C

[0169] Under a nitrogen atmosphere, 177 g of dry PPG (Mn = 2000) and 50 g of IPDI were added to a three-necked flask equipped with a thermometer, reflux condenser, and stir bar. The reaction was carried out at 90 °C for 3 h. Then, 8.5 g of DMPA and 11 g of 2,2,3,3-tetrafluoro-1,4-butanediol were added, along with an appropriate amount of acetone to adjust the viscosity of the system to 3000 mPa·s. The reaction was then carried out at 70 °C for 5 h. After the reaction was completed, water was added for emulsification under high-speed stirring. LiOH solution was then added dropwise to neutralize the emulsion to pH = 7. The acetone in the emulsion was then removed by vacuum distillation to obtain modified polyurethane slurry C. Modified polyurethane slurry C had a solid content of 30 wt.%, an F content of 2.1 wt.%, and a Li content of 0.18 wt.%.

[0170] Example D

[0171] Under a nitrogen atmosphere, 177 g of dry PPG (Mn = 2000) and 50 g of IPDI were added to a three-necked flask equipped with a thermometer, reflux condenser, and stir bar. The reaction was carried out at 90 °C for 3 h. Then, 8.5 g of DMPA and an appropriate amount of acetone were added to adjust the viscosity of the system to 3000 mPa·s, and the reaction was carried out at 70 °C for 5 h. After the reaction was completed, water was added for emulsification under high-speed stirring. LiOH solution was then added dropwise to neutralize the emulsion to pH = 7. The acetone in the emulsion was then removed by vacuum distillation to obtain modified polyurethane slurry D, which had a solid content of 30 wt.% and a Li content of 0.18 wt.%.

[0172] Example E

[0173] Under a nitrogen atmosphere, 177 g of dry PPG (Mn = 2000) and 50 g of IPDI were added to a three-necked flask equipped with a thermometer, reflux condenser, and stir bar. The reaction was carried out at 90 °C for 3 h. Then, 11 g of 2,2,3,3-tetrafluoro-1,4-butanediol and an appropriate amount of acetone were added to adjust the viscosity of the system to 3000 mPa·s, and the reaction was carried out at 70 °C for 5 h. After the reaction was completed, water was added for emulsification under high-speed stirring, and then the acetone in the emulsion was removed by vacuum distillation to obtain modified polyurethane slurry C. The solid content of modified polyurethane slurry C was 30 wt.%, and the F content was 2.16 wt.%.

[0174] Example 1

[0175] (1) Preparation of the first negative electrode slurry: 3640g QC-8, 200g silicon carbide, 32g SP, and 800g single-walled CNT dispersion (solid content of 1wt.%) were mixed and dry-mixed for 15min at 30r. 400g modified polyurethane slurry A (solid content of 30wt.%, F content of 1.3wt.%, Li content of 0.25wt.%) and 3584g water were added. The mixture was rotated at 3000r and 30r at 120min to fully mix and disperse, and the first negative electrode slurry was obtained. The solid content of the first negative electrode slurry was 46wt.%, and the discharge viscosity was 3000mpa·s.

[0176] (2) Preparation of the first negative electrode film: Take a carbon-coated copper foil with a conductive carbon black layer of 0.5 μm thickness on both sides of the copper foil. The thickness of the carbon-coated copper foil is 8 μm. The first negative electrode slurry obtained in step (1) is uniformly coated on both sides of the carbon-coated copper foil to obtain the first negative electrode film. The coating amount of the first negative electrode film is 100 g / m. 2 .

[0177] (3) Preparation of the second negative electrode slurry: 3636.8g QC-8, 200g silicon carbon, 34.6g SP, and 864g single-walled CNT dispersion (solid content of 1wt.%) were mixed and dry-mixed for 15min at 30r. 400g modified polyurethane slurry B (solid content of 30wt.%, F content of 2.1wt.%, Li content of 0.18wt.%) and 3517.092g water were added. The mixture was rotated at 3000r and 30r at 30r for 180min to fully mix and disperse, thus obtaining the second negative electrode slurry. The solid content of the second negative electrode slurry was 40wt.%, and the discharge viscosity was 3000mpa·s.

[0178] (4) Preparation of the second negative electrode film: The second negative electrode slurry obtained in step (3) is uniformly coated on both sides of the first negative electrode film to obtain the second negative electrode film. The coating amount of the second negative electrode film is 100 g / m. 2 .

[0179] The total coating amount of the negative electrode film is 200 g / m 2 .

[0180] (5) Preparation of negative electrode sheet

[0181] The electrode obtained in step (4) is prepared according to a ratio of 1.65 g / cm³. 3 The compaction density is then rolled to obtain the negative electrode sheet.

[0182] (6) Preparation of positive electrode slurry: 2901g of high-nickel octet ternary NCM (LiMn) was prepared. 0.8 Co 0.1 Mn 0.1 278g of multi-walled carbon nanotube dispersion (solid content of 5.4wt.%), 30g of SP, and 54g of PVDF were added to 7000g of NMP. After 3000r self-rotation and 120min of thorough mixing and dispersion, a positive electrode slurry was obtained. The solid content of the positive electrode slurry was 70wt.%, and the discharge viscosity was 6000mpa·s.

[0183] (7) Preparation of positive electrode film

[0184] The positive electrode slurry obtained in step (6) is coated on both sides onto a smooth aluminum foil with a thickness of 12 μm to obtain a positive electrode film. The total coating weight of the positive electrode film is 368 g / m. 2 .

[0185] (8) Preparation of positive electrode sheet

[0186] The electrode obtained in step (7) is rolled at a compaction density of 3.45 g / cm3 to obtain the positive electrode.

[0187] (9) Lithium-ion battery assembly

[0188] The negative and positive electrode sheets are cut and die-cut separately. Then, the cut positive electrode sheet, the cut negative electrode sheet, and the separator are stacked to form a bare cell, and positive and negative electrode tabs are laser-welded to the positive and negative electrodes respectively.

[0189] The wound battery cells are then encapsulated and welded, and then placed in a vacuum oven at 90°C for 36 hours. After baking, the cells are injected with electrolyte. The electrolyte injection coefficient is 4. The electrolyte-injected battery is then left to stand for 24 hours before being sealed and welded.

[0190] (10) Cell formation

[0191] The cell formation process begins with low-current charging, using 0.05C, 0.1C, and 0.2C sequentially until the cell capacity reaches 40%. After resting for 24 hours, the cell is then divided into two phases: a charging current of 0.5C and a discharging current of 0.5C, with a range of 2.5 to 4.2V.

[0192] Example 2

[0193] The preparation method in this embodiment is the same as in Example 1, except that the double-sided coating amount of the first negative electrode film is 135 g / m. 2 The double-sided coating amount of the second negative electrode film is 65 g / m. 2 .

[0194] Example 3

[0195] The preparation method in this embodiment is the same as in Example 1, except that the double-sided coating amount of the first negative electrode film is 65 g / m. 2 The double-sided coating amount of the second negative electrode film is 135 g / m. 2 .

[0196] Example 4

[0197] The preparation method of this embodiment is the same as that of Example 1, except that in the preparation of the first negative electrode slurry, the mass of QC-8 is 3490g, the mass of modified polyurethane slurry A is 533.333g, and the mass of water is 3490g; in the preparation of the second negative electrode slurry, the mass of QC-8 is 3656.8g, the mass of modified polyurethane slurry B is 333.333g, and the mass of water is 3563.759g.

[0198] Example 5

[0199] The preparation method of this embodiment is the same as that of Example 1, except that in the preparation of the first negative electrode slurry, the mass of QC-8 is 3630g, the mass of modified polyurethane slurry A is 333.333g, and the mass of water is 3490g; in the preparation of the second negative electrode slurry, the mass of QC-8 is 3596.8g, the mass of modified polyurethane slurry B is 533.333g, and the mass of water is 3423.759g.

[0200] Example 6

[0201] The preparation method in this embodiment is the same as in Example 1, except that in the preparation of the first negative electrode slurry, the mass of QC-8 is 3720g and the mass of silicon carbon is 120g; in the preparation of the second negative electrode slurry, the mass of QC-8 is 3192g, the mass of silicon carbon is 600g, the mass of SP is 38.4g, the mass of single-walled CNT dispersion is 960g, the mass of modified polyurethane slurry B is 533.333g, and the mass of water is 3323.919g; in addition, the total coating amount of the positive electrode film is 420g / m 2 .

[0202] Example 7

[0203] The preparation method of this embodiment is the same as that of Example 1. The difference is that in the preparation of the second negative electrode slurry, ordinary polyurethane slurry WH1750 (solid content of 30wt.%) without F and Li modification is used instead of modified polyurethane slurry B.

[0204] Example 8

[0205] (1) Preparation of negative electrode slurry: 3640g QC-8, 200g silicon carbide, 32g SP, and 800g single-walled CNT dispersion (solid content of 1wt.%) were mixed and dry-mixed for 15min at 30r. 400g modified polyurethane slurry C (solid content of 30wt.%, F content of 2.1wt.%, and Li content of 0.18wt.%) and 3584g water were added. The mixture was rotated at 3000r and 30r at 120min to fully mix and disperse, and the negative electrode slurry was obtained. The solid content of the negative electrode slurry was 46wt.%, and the discharge viscosity was 3000mpa·s.

[0206] (2) Preparation of the negative electrode film: Take a carbon-coated copper foil with a conductive carbon black layer of 0.5 μm thickness on both sides of the copper foil. The thickness of the carbon-coated copper foil is 8 μm. Coat the negative electrode slurry obtained in step (1) uniformly on both sides of the carbon-coated copper foil to obtain the negative electrode film. The total coating amount of the negative electrode film is 200 g / m. 2 .

[0207] (3) Preparation of negative electrode sheet

[0208] The electrode obtained in step (2) is prepared according to a ratio of 1.65 g / cm³. 3 The compaction density is then rolled to obtain the negative electrode sheet.

[0209] The subsequent preparation of the positive electrode and battery assembly are the same as in Example 1.

[0210] Comparative Example 1

[0211] (1) Preparation of negative electrode slurry: 40g CMC was dissolved in 3438g water and dispersed into a clear solution by rotating at 3000r for 30min. 3640g QC-8, 200g silicon carbide, 32g SP, and 800g single-walled CNT dispersion (solid content of 1wt.%) were added and the mixture was rotated at 30r for 15min. After being fully stirred and dispersed by rotating at 3000r and 30r for 120min, 1330g PAA (solid content of 6%) was added and the mixture was fully stirred and dispersed by rotating at 3000r and 30r for 60min to obtain the negative electrode slurry. The solid content of the negative electrode slurry was 42wt.%, and the discharge viscosity was 4000mpa·s.

[0212] (2) Preparation of negative electrode sheet: Take a carbon-coated copper foil with a conductive carbon black layer of 0.5 μm thickness on both sides of the copper foil. The thickness of the carbon-coated copper foil is 8 μm. Coat the negative electrode slurry obtained in step (1) uniformly on both sides of the carbon-coated copper foil to obtain the negative electrode film. The total coating amount of the negative electrode film is 200 g / m. 2 .

[0213] (3) The electrode obtained in step (2) is prepared according to a ratio of 1.65 g / cm³. 3 The compaction density is then rolled to obtain the negative electrode sheet.

[0214] The subsequent preparation of the positive electrode sheet, battery assembly, and cell formation are the same as in Example 1.

[0215] Comparative Example 2

[0216] The preparation method of this comparative example is the same as that of Example 1, except that in the preparation of the first negative electrode slurry, ordinary polyurethane slurry WH1750 (solid content of 30 wt.%) without F and Li modification is used instead of modified polyurethane slurry A, and in the preparation of the second negative electrode slurry, ordinary polyurethane slurry WH1750 (solid content of 30 wt.%) without F and Li modification is used instead of modified polyurethane slurry B.

[0217] Table 1. The structures of the modified polyurethanes in Examples A to G are shown in Table 1.

[0218]

[0219] Table 2. Composition and content of the negative electrode film in Examples 1-8 and Comparative Examples 1-2

[0220]

[0221]

[0222] Performance testing:

[0223] (1) Adhesion test method: Cut the rolled negative electrode sheet into 25cm×20cm samples, and use Nitto 2cm wide double-sided tape to stick it to the back of the steel plate. Roll it back and forth three times with a 2kg roller, fix the steel plate on a tensile testing machine (Instron 3343 sensor range 1~10N), clamp one end of the negative electrode sheet sample on the tensile testing machine sensor, peel angle of the negative electrode sheet sample is 180°, tensile speed is 5cm / min, and peel the negative electrode sheet sample off the double-sided tape. The adhesion test results of the negative electrode film layers of each embodiment and comparative example are shown in Table 3.

[0224] (2) Cohesive strength test method: Cut the rolled negative electrode sheet into 3cm×15cm samples. Use 3M 3cm wide double-sided tape to adhere to the back of the steel plate, and use 2cm wide transparent tape to adhere to the front of the negative electrode sheet sample. Roll the sample back and forth three times with a 2kg roller. Fix the steel plate on a tensile testing machine (Instron 3343, sensor range 1~10N). Peel 1~2cm of the transparent tape from the negative electrode sheet sample. Clamp one end of the transparent tape to the tensile testing machine sensor. The peeling angle is 180°, and the tensile speed is 5cm / min. Peel the tape off the surface of the negative electrode sheet sample. The cohesive strength test results of the negative electrode film layers in each embodiment and comparative example are shown in Table 3.

[0225] (3) Physical rebound test method: The negative electrode sheet was rolled to the designed thickness. A 20cm long negative electrode sheet was taken and baked in a 90℃ oven for 48 hours. Then it was taken out, avoiding the thinned areas on both sides. The thickness was measured at 15 test points on the negative electrode sheet using a Mitutoyo micrometer. The average thickness of the negative electrode sheet after baking was calculated. Physical rebound = average thickness of the negative electrode sheet after baking / designed rolling thickness of the negative electrode sheet. The physical rebound test results of the negative electrode film layers of each embodiment and comparative example are shown in Table 3.

[0226] (4) Full-charge rebound test method: The assembled battery was charged to a full charge of 3.65V, disassembled in a dehumidified environment with a dew point of -20°C, and the negative electrode sheet was removed. A Mitutoyo micrometer was used to measure the thickness at 12 test points on the fully charged yellow double-sided portion of the negative electrode sheet. The average thickness of the negative electrode sheet after full charge was calculated. Full-charge rebound = average thickness of the negative electrode sheet after full charge / designed rolling thickness of the negative electrode sheet. The full-charge rebound test results of the negative electrode film layers in each embodiment and comparative example are shown in Table 3.

[0227] (5) Gas production test method during formation: water displacement method. An electronic balance is placed on an iron frame above a 3L container filled with 25°C deionized water. The battery before formation is suspended from the sensor below the electronic balance using clamps and wire, and then immersed in the 25°C water. The weight before formation is calibrated as M1. After formation, the battery is calibrated using the same equipment, method, and immersion water level, and the weight is M2. Gas production during formation = M1 - M2 / battery design capacity. The gas production during formation of the cells in each embodiment and comparative example is shown in Table 3.

[0228] (6) Negative electrode film internal resistance test method: The rolled negative electrode sheet is cut into 20cm long negative electrodes. Ten points are randomly selected on the coated area of ​​the electrode sheet, and the resistance at these points is measured at 25°C using an ACCFILM four-probe film resistance meter (TT-ACCF-G2A). The average value of the ten values ​​is the negative electrode film internal resistance. The internal resistance test results of the negative electrode film of each embodiment and comparative example are shown in Table 4.

[0229] (7) Battery capacity grading and first-efficiency test method: In the formation process, a small current is used for initial charging, followed by charging at 0.05C, 0.1C, and 0.2C sequentially until 40% of the cell capacity is reached. After resting for 24 hours, capacity grading is performed. The capacity grading charging current is 0.5C, and the discharging current is 0.5C, with a range of 2.5 to 4.2V. The first-efficiency calculation method is capacity grading discharge capacity / (capacity grading charging capacity + formation charging capacity)%. The battery capacity grading and first-efficiency test results of each embodiment and comparative example are shown in Table 5.

[0230] (8) Battery cycle performance test method: A Nebula charge / discharge machine (5V 60A) was used in a 25℃ constant temperature chamber. The battery's nominal capacity of 5.0Ah at 1C was used as the test benchmark. The battery was fully charged at 2C and discharged at 1C. The voltage range was 2.5 to 4.2V. The average value of 5 batteries in each group was taken as the battery capacity. The capacity retention rate of the batteries in each embodiment and comparative example after 150 cycles and 300 cycles is shown in Table 6.

[0231] Table 3. Performance test results of negative electrode film and battery cell in Examples 1-8 and Comparative Examples 1-2

[0232] Adhesion Cohesion Physical rebound % Full charge rebound % Gas production rate (g / Ah) Example 1 14 19 4.7 25.4 0.43 Example 2 13.7 18.5 6.7 27.8 0.68 Example 3 14.1 19.5 3.6 23.3 0.38 Example 4 16.2 16.8 4.5 25.7 0.74 Example 5 12.2 22.5 5.1 25.2 0.39 Example 6 12.5 21.2 5.6 29.4 0.86 Example 7 13.5 14.2 6.5 27.6 1.27 Example 8 14.2 16.3 4.4 26 0.61 Comparative Example 1 11.3 16 7.2 28.4 2.38 Comparative Example 2 10.2 12.2 8.6 30.3 2.01

[0233] The results from Example 8 and Comparative Example 1 show that using modified polyurethane instead of the conventional CMC+PAA binder system improves the adhesion between the negative electrode film and the foil, as well as the cohesive force of the negative electrode film. This is mainly due to the lithium-ionized functional group -COO in the modified polyurethane. - Li +This modification enhances the adhesion between the polyurethane and the foil, as well as the cohesion of the negative electrode film, thus strengthening the binding of the negative electrode material. Furthermore, the strong polarity of the CF bonds in the modified polyurethane makes it less prone to breakage after film formation, which is beneficial for maintaining adhesion and binding the negative electrode material during rolling. The reduced physical rebound and full-charge rebound of the negative electrode sheet also demonstrate that the negative electrode material is in a well-binded state. The results of Example 8 and Comparative Example 1 also show that using modified polyurethane instead of the conventional CMC+PAA binder system reduces the gas production during cell formation. This is because, on the one hand, polyurethane contains almost no -OH functional groups, which reduces side reactions with the electrolyte compared to CMC and PAA. On the other hand, F has poor affinity for water; introducing F to modify polyurethane effectively reduces the affinity of the negative electrode film for water, reducing water adsorption and thus reducing side reactions between the negative electrode film and the electrolyte.

[0234] The results from Example 1 and Comparative Example 2 show that using modified polyurethane instead of the ordinary polyurethane adhesive system improves the adhesion between the negative electrode film and the foil, as well as the cohesive force of the negative electrode film. This is because, on the one hand, the lithium-ion functional group -COO in the modified polyurethane... - Li + It can improve the adhesion between the foil and the cohesion of the negative electrode film, and enhance the binding of the negative electrode material. On the other hand, the CF bond in the modified polyurethane is highly polar and is not easy to break after film formation, which is conducive to maintaining the adhesion during the rolling process and the charging and discharging process. The physical rebound and full-charge rebound of the negative electrode sheet are reduced.

[0235] As can be seen from the results of Example 7 and Comparative Example 2, by using modified polyurethane instead of ordinary polyurethane adhesive system only in the first negative electrode film layer, the adhesion between the negative electrode film layer and the foil and the cohesion of the negative electrode film layer are also improved.

[0236] The results from Examples 1 and 8 show that replacing the single-layer negative electrode film with a bilayer design, and adjusting the F content in the second negative electrode film to be greater than that in the first negative electrode film, can improve the cohesion of the negative electrode film and reduce the amount of gas produced during formation. This is because the surface F content of the bilayer negative electrode film is higher than that of the single-layer design, resulting in a lower affinity for water, less water adsorption, and fewer side reactions with the electrolyte, thus leading to a lower amount of gas produced during formation.

[0237] The first and second negative electrode slurries used in Examples 1 and 2-3 were the same, except that the coating amount of the two slurries was different, resulting in different total F content and F ratio in the negative electrode films obtained from these three examples. The results from Examples 1 and 2-3 show that, when the total F content is not significantly different, increasing the F ratio in the bilayer negative electrode film is beneficial for reducing the amount of gas produced during formation.

[0238] Table 4. Resistance of the negative electrode film in Examples 1-8 and Comparative Examples 1-2

[0239] category Negative electrode film resistance (mΩ) Example 1 3.5 Example 2 2.7 Example 3 5.4 Example 4 2.2 Example 5 4.8 Example 6 5.9 Example 7 6.5 Example 8 4.2 Comparative Example 1 8.8 Comparative Example 2 6.7

[0240] A comparison of Example 8 and Comparative Example 1 shows that replacing the conventional CMC+PAA binder system with modified polyurethane significantly reduces the internal resistance of the negative electrode film. This is because the modified polyurethane possesses the lithium-ion functional group -COO. - Li + This can improve the conductivity of the negative electrode film and reduce its internal resistance.

[0241] A comparison of Example 1 and Comparative Example 2 shows that replacing the ordinary polyurethane binder with modified polyurethane significantly reduces the internal resistance of the negative electrode film. This is mainly because the modified polyurethane has a lithium-ion functional group -COO. - Li + This can improve the conductivity of the negative electrode film and reduce its internal resistance.

[0242] The results from Examples 1 and 8 show that the resistance of the negative electrode film in Example 1 is lower than the internal resistance of the negative electrode film in Example 8. This is directly related to the optimization of the content of modified element Li in the first and second negative electrode films during the design of the double-layer coating. In Example 1, the first negative electrode film near the foil adopts a high-lithium design, while the second negative electrode film near the outside adopts a low-lithium design. Therefore, the conductivity of the negative electrode film can be more effectively balanced, and the internal resistance of the negative electrode film can be reduced.

[0243] The first and second negative electrode slurries used in Examples 1 and 2-3 were the same, except that the coating amount of the two slurries was different, resulting in different total Li content and Li ratio in the negative electrode films obtained from these three examples. The results from Examples 1 and 2-3 show that, when the total Li content is not significantly different, adjusting the Li ratio in the bilayer negative electrode film to reduce its internal resistance is beneficial.

[0244] Table 5. First efficiency of batteries in Examples 1-8 and Comparative Examples 1-2

[0245] category First-efficacy (%) Example 1 87.7 Example 2 86.0 Example 3 87.8 Example 4 87.2 Example 5 86.5 Example 6 85.9 Example 7 84.5 Example 8 86.3 Comparative Example 1 83.2 Comparative Example 2 84.3

[0246] A comparison of Example 8 and Comparative Example 1 shows that replacing the conventional CMC+PAA binder system with modified polyurethane significantly improves the battery's first-cycle efficiency during capacity testing. This is partly because the modified polyurethane increases the adhesion between the negative electrode film and the foil, reducing the expansion and cracking of the negative electrode particles during the first charge-discharge process, thus minimizing the loss of active lithium. Another reason is the introduction of the lithium-ion functional group -COO into the modified polyurethane. - Li + This provides additional lithium replenishment during the initial charge and discharge cycle.

[0247] A comparison of Example 1 and Comparative Example 2 shows that replacing ordinary polyurethane binder with modified polyurethane significantly improves the battery's first-cycle efficiency during capacity testing. This is partly due to the enhanced adhesion resulting from the double-layer design and modification, which reduces the expansion and cracking of the silicon-carbon anode particles during the first charge-discharge process, thus minimizing the loss of active lithium. Additionally, the introduction of the lithium-ionized functional group -COO into the modified polyurethane further contributes to this improvement. - Li + This provides additional lithium replenishment during the initial charge and discharge cycle.

[0248] Table 6. Cycle performance of batteries from Examples 1-8 and Comparative Examples 1-2

[0249]

[0250] The comparison between Example 8 and Comparative Example 1 shows that the battery has significantly better cycle performance after replacing the conventional CMC+PAA binder system with modified polyurethane. The main reason is that the modified polyurethane enhances the adhesion between the negative electrode film and the foil and the cohesion of the negative electrode film, reducing the pulverization of the negative electrode material during cycling.

[0251] The comparison between Example 1 and Comparative Example 2 shows that the battery cycle performance is significantly better when modified polyurethane is used instead of ordinary polyurethane binder. The main reason is that modified polyurethane enhances the adhesion between the negative electrode film and the foil and the cohesion of the negative electrode film, reducing the pulverization of the negative electrode material during cycling.

[0252] A comparison of Examples 1 and 8 shows that batteries with a dual-layer design have better cycle performance than batteries with a single-layer design. This is because dual-layer cells can regulate the adhesion and ion transport balance between the inner and outer electrode layers by improving the adhesive modification and active functional group content in the inner and outer coating layers. The outer layer is closer to the electrolyte, resulting in better wetting and lithium-ion kinetics. Therefore, the negative electrode can be charged and discharged more deeply, requiring stronger cohesion and adhesion. The inner layer is closer to the inner foil, resulting in weaker kinetics. It requires good conductivity and stronger adhesion to the foil. This differentiated design of dual-layer adhesive modification can maximize the balance between the advantages and disadvantages of the inner and outer negative electrode layers, extending their cycle life.

[0253] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0254] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A modified polyurethane, characterized in that, The modified polyurethane contains CF bonds and / or -COO bonds. - Li + Polyurethane.

2. The modified polyurethane according to claim 1, characterized in that, When the modified polyurethane is a polyurethane containing CF bonds, the structure of the modified polyurethane is as follows: Where n = 2 to 56; When the modified polyurethane contains -COO - Li + When using polyurethane, the structure of the modified polyurethane is shown in the following formula: Where n = 2 to 56; When the modified polyurethane contains CF bonds and -COO - Li + When using polyurethane, the structure of the modified polyurethane is shown in the following formula: Where n = 2 to 56.

3. The modified polyurethane according to claim 1 or 2, characterized in that, The content of F element is 2 wt.% to 7 wt.% based on 100 wt.% of the total mass of the modified polyurethane; and / or, the content of Li element is 1.2 wt.% to 4 wt.% based on 100 wt.% of the total mass of the modified polyurethane.

4. The method for preparing modified polyurethane according to any one of claims 1 to 3, characterized in that, When the modified polyurethane is a polyurethane containing CF bonds, the preparation method includes the following steps: S1-1. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer; S2-1. The first prepolymer, chain extender, fluorinated butanediol and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer; S3-1. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; the solvent in the emulsion is removed by distillation to obtain the modified polyurethane; When the modified polyurethane is a polyurethane containing lithium functional groups, the preparation method includes the following steps: S1-2. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer; S2-2. The first prepolymer, chain extender and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer; S3-2. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; then LiOH is added dropwise to the emulsion until the pH of the emulsion is neutral, and then the solvent in the emulsion is removed by distillation to obtain the modified polyurethane; When the modified polyurethane is a polyurethane containing CF bonds and lithium functional groups, the preparation method includes the following steps: S1-3. Under a nitrogen atmosphere, isophorone diisocyanate and polyoxypropylene glycol are mixed and polymerized to obtain the first prepolymer; S2-3. The first prepolymer, chain extender, fluorinated butanediol and solvent are mixed and then subjected to a chain extension reaction to obtain the second prepolymer; S3-3. The second prepolymer is mixed with water and then emulsified to obtain an emulsion; then LiOH is added dropwise to the emulsion until the pH of the emulsion is neutral, and then the solvent in the emulsion is removed by distillation to obtain the modified polyurethane.

5. The preparation method according to claim 4, characterized in that, The polymerization reaction is carried out at a temperature of 80–100°C for a duration of 2–5 h; and / or the chain extension reaction is carried out at a temperature of 60–90°C for a duration of 4–6 h.

6. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, a binder, and an optional conductive agent. The negative electrode active material includes a silicon-based material, and the binder includes the modified polyurethane according to any one of claims 1 to 3.

7. The negative electrode sheet according to claim 6, characterized in that, The content of F element in the negative electrode film is 0.10 g / m 2 ~0.16g / m 2 And / or, the Li element content in the negative electrode film is 0.008 g / m 2 ~0.013g / m 2 .

8. The negative electrode sheet according to claim 6 or 7, characterized in that, Based on a total mass of 100 wt.% for the negative electrode film, the content of the silicon-based material is 3 wt.% to 15 wt.%, and / or the content of the conductive agent is 0.5 wt.% to 1.5 wt.%.

9. The negative electrode sheet according to claim 6, characterized in that, The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, a first binder, and optionally a first conductive agent. The second negative electrode film layer includes a second negative electrode active material, a second binder, and optionally a second conductive agent. The first negative electrode active material includes a first silicon-based material, and / or the first binder includes a first modified polyurethane, and / or the second negative electrode active material includes a second silicon-based material, and / or the second binder includes a second modified polyurethane.

10. The negative electrode sheet according to claim 9, characterized in that, The content of F element in the first negative electrode film layer is 0.02 g / m 2 ~0.06g / m 2 ; and / or, the F element content in the second negative electrode film is 0.05 g / m 2 ~0.12g / m 2 ; and / or, the ratio of the content of F element in the second negative electrode film to the content of F element in the first negative electrode film is 1 to 5; And / or, the Li content in the first negative electrode film is 0.004 g / m 2 ~0.011g / m 2 ; and / or, the Li content in the second negative electrode film is 0.002 g / m 2 ~0.005g / m 2 ; and / or, the ratio of the Li element content in the second negative electrode film to the Li element content in the first negative electrode film is 0.18 to 0.

90.

11. The negative electrode sheet according to claim 9 or 10, characterized in that, Based on a total mass of 100 wt.% for the first negative electrode film, the content of the first silicon-based material in the first negative electrode film is 3 wt.% to 8 wt.%; and / or, based on a total mass of 100 wt.% for the second negative electrode film, the content of the second silicon-based material in the second negative electrode film is 4 wt.% to 16 wt.%; and / or, the ratio of the content of the second silicon-based material in the second negative electrode film to the content of the first silicon-based material in the first negative electrode film is 1 to 3.

12. The negative electrode sheet according to claim 9 or 10, characterized in that, Based on a total mass of 100 wt.% of the first negative electrode film, the content of the first conductive agent in the first negative electrode film is 0.9 wt.% to 1.1 wt.%; and / or, based on a total mass of 100 wt.% of the second negative electrode film, the content of the second conductive agent in the second negative electrode film is 1.0 wt.% to 1.5 wt.%; and / or, the ratio of the content of the second conductive agent in the second negative electrode film to the content of the first conductive agent in the first negative electrode film is 1.05 to 1.

5.

13. A secondary battery, characterized in that, The secondary battery includes the negative electrode sheet as described in any one of claims 6 to 12.

14. An electrical appliance, characterized in that, The electrical device includes the secondary battery as described in claim 13.

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