Flexible agent and preparation method thereof, positive pole piece and preparation method thereof, battery monomer, battery and electric equipment

Abstract

The invention provides a flexible agent and a preparation method thereof, a positive pole piece and a preparation method thereof, a battery monomer, a battery and electric equipment, and belongs to the technical field of batteries. The flexible agent disclosed by the invention is formed by polymerizing diisocyanate and dihydric alcohol containing siloxane groups. A diisocyanate part in a molecular chain of the flexible agent cannot spin due to a double-bond effect and is used as a hard segment part to act as an anchoring group; a siloxane-containing part in a molecular chain of the flexible agent can freely rotate to serve as a soft segment part due to a covalent bond, and siloxane can form a relatively strong intermolecular acting force with a binder and an active material in the active material layer, so that the dispersibility of the active material and the binder is improved, and the stability of a system is maintained; and meanwhile, the flexible agent can be uniformly dispersed in the system, the strong hydrogen-bond interaction between molecules of the high-molecular binder is reduced, and good flexibility is provided for the pole piece, so that the flexibility of the pole piece is improved, and the phenomenon that the pole piece is fragile and easy to break in the processes of winding, hot pressing and the like is reduced or avoided.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a flexible agent and its preparation method, a positive electrode sheet and its preparation method, a battery cell, a battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on its energy density, cycle performance, and safety performance.

[0003] In the electrode preparation process, the electrode is usually prepared by a winding process. If the electrode is not flexible enough, the inner circle of the electrode will crack at the corner during the winding process, resulting in a decrease in cell performance. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a flexible agent and its preparation method, a positive electrode sheet and its preparation method, a battery cell, a battery and an electrical device, which can effectively improve the flexibility of the electrode sheet and reduce or avoid the phenomenon of brittle breakage of the electrode sheet during winding, hot pressing and other processes.

[0005] To achieve the above objectives, a first aspect of this application provides a flexibility agent comprising a compound having the following structural formula:

[0006]

[0007] R1 is selected from C 2～10 straight-chain alkylene or Among them, R3, R4, R5, and R6 are all independently selected from H and C. 2～8 ester group, C 2～8 sulfonate group, C 2～8 sulfonates, C 2～8 The amide group or -(CH2-CH2-O)n1-, where n1 is 3 to 6; R2 includes Si-O-Si groups, where x is 3 to 70.

[0008] Therefore, in the flexible agent with the above structural formula, the diisocyanate portion of the molecular chain, due to the double bond interaction, cannot spin and acts as an anchoring group in the hard segment. The diisocyanate is highly polar and can adsorb or embed into the binder molecular chain in the active material layer, enhancing the stretching of the binder molecular chain. The siloxane portion of the flexible agent's molecular chain, due to its covalent bond, can rotate freely and acts as a soft segment. Furthermore, the siloxane can form strong intermolecular forces with the binder and active material in the active material layer, thereby increasing the dispersibility of the active material and binder and maintaining the stability of the system. Simultaneously, the flexible agent can be uniformly dispersed in the system, reducing the strong hydrogen bonding between polymer binder molecules, providing good flexibility for the electrode, thus improving the electrode's flexibility and reducing or avoiding brittle breakage during winding and hot pressing. In addition, the lone pair electrons of the oxygen atoms in the flexible agent can coordinate with lithium ions, promoting lithium ion transport, reducing battery impedance, and improving the battery's electrochemical performance.

[0009] In any embodiment, the Si-O-Si groups in R2 are located at the ends and / or in the chain. When the Si-O-Si groups in R2 are located in the chain, R2 has no side groups or the number of carbons in the side groups is 1 to 5. By placing the Si-O-Si groups in R2 at the ends, the siloxane can rotate freely, thereby improving the flexibility of the electrode and reducing or avoiding the brittle fracture of the electrode during winding, hot pressing, etc.; by placing the Si-O-Si groups in R2 in the chain, and R2 having no side groups or the number of carbons in the side groups is 1 to 5, the rotational resistance of the siloxane is small, allowing it to rotate freely, thereby improving the flexibility of the electrode and reducing or avoiding the brittle fracture of the electrode during winding, hot pressing, etc.

[0010] In any implementation, R2 includes any one of the following structures:

[0011]

[0012]

[0013] Where a is 13–30, b is 2–10, c is 2–20, d is 2–20, and e is 10–50; R7 is selected from C. 2～12 Straight-chain alkylene groups or -(CH2-CH2-O)n2-, where n2 is 2 to 6; R8 and R9 are each independently selected from C 1～5 Alkyl group; R 10 Selected from C 1～5 Alkyl, C 1～5 Alkoxy, C 1～5 alkylthio or C 1～5 Siloxane; R 11 Selected from C 1～5 Alkyl, C 1～5 Alkoxy or C 1～5Alkylthio; R 12 Selected from C that has been substituted with one or more hydroxyl groups 2～5 Alkyl groups. By selecting the above structure for R2, siloxanes have lower rotational resistance and can rotate freely, thereby improving the flexibility of the electrode and reducing or avoiding brittle breakage of the electrode during winding and hot pressing.

[0014] In any implementation, the above-described R 10 Selected from -CH2Si(OCH3)3, -CH2CH2Si(OCH3)3, -CH2CH2CH2Si(OCH3)3, -(CH2)4Si(OCH3)3, -(CH2)5Si(OCH3)3, -CH2Si(OCH2CH3)3, -(CH2)2Si(OCH2CH3)3, -(CH2)3Si(OCH2CH3)3, -CH2OCH2Si(OCH3)3, -CH2O(CH2)2Si(OCH3)3, -CH2O(CH2)2Si(OCH3)3 or -CH2O(CH2)3Si(OCH3)3.

[0015] In any implementation, the above-described R 12 Selected from -CH(CH2OH)CH2CH2OH, -CH(CH2OH)CH2CH2CH2OH or -CH(CH2CH2OH)CH2CH2OH.

[0016] In any embodiment, R3, R4, R5, and R6 are each independently selected from -COOCH3, -COOCH2CH3, -COO(CH2)2CH3, -COO(CH2)3CH3, -COO(CH2)4CH3, -CH2COOCH2CH3, -CH2COO(CH2)2CH3, -CH2COO(CH2)3CH3, -(CH2)2COO(CH2)3CH3, -SO3CH3, -SO3CH2CH3, -SO3(CH2)2CH3, -SO3(CH2)3CH3, -SO3(CH2)4CH3, -CH2SO3CH2CH3, -CH2SO3(CH2)2CH3, -CH2SO3(CH2)3CH3, -(CH2)2SO3CH3, -(CH2)2SO3CH2CH3, -(CH2)2SO3(CH2)2CH3, -(CH2)2SO3(CH2)2CH3, - SO2CH3, -SO2CH2CH3, -SO2(CH2)2CH3, -SO2(CH2)3CH3, -SO2(CH2)4CH3, -CH2SO2CH2CH3, -CH2S O2(CH2)2CH3, -CH2SO2(CH2)3CH3, -(CH2)2SO2CH3, -(CH2)2SO2CH2CH3, -(CH2)2SO2(CH2)2CH3, -SO3A, -CONHCH3, -CONHCH2CH3, -CONH(CH2)2CH3, -CONH(CH2)3CH3, -CONH(CH2)4CH3, -CH2CONHCH2CH3, -CH2CONH(CH2)2CH3, -CH2CONH(CH2)3CH3 or -(CH2)2CONH(CH2)3CH3, where A includes Li, Na, K, or Mg.

[0017] In any embodiment, R3, R4, R5, and R6 are not simultaneously H. By making R3, R4, R5, and R6 not simultaneously H, at least one of R3, R4, R5, and R6 is selected from C. 2～8 ester group, C 2～8 sulfonate group, C 2～8 sulfonates, C 2～8 The amide group or -(CH2-CH2-O)n1-, where n1 is 3 to 6, wherein the ester group increases the affinity with the electrolyte and increases the electrolyte wetting rate, while the sulfonate group, sulfonate, amide group and ether can provide lithium ion channels, promote lithium ion transport, and thus improve battery kinetics.

[0018] In any embodiment, the viscosity-average molecular weight of the flexible agent is 1000–16000. By keeping the viscosity-average molecular weight of the flexible agent within this range, it is possible to achieve a dispersing effect with a small addition amount without affecting the battery energy density, while maintaining low viscosity and good reactivity, and essentially not affecting the lithium-ion migration kinetics in the electrode. A flexible agent with a viscosity-average molecular weight of 1000–16000 can effectively improve the flexibility of the electrode and the electrochemical performance of the battery.

[0019] A second aspect of this application provides a method for preparing a flexibility agent, comprising: reacting a starting material containing a diisocyanate, a siloxane-containing diol, a solvent, and a catalyst. The diisocyanate has the structural formula OCN-R1-NCO, where R1 is selected from C... 2～10 straight-chain alkylene or Among them, R3, R4, R5, and R6 are all independently selected from H and C. 2～8 ester group, C 2～8 sulfonate group, C 2～8 sulfonates, C 2～8 The amide group or -(CH2-CH2-O)n1-, where n1 is 3 to 6. The structural formula of a diol containing a siloxane group is HO-R2-OH, where R2 includes a Si-O-Si group.

[0020] Therefore, the synthesis method of this application is simple, the synthesized flexible agent has a stable structure, a viscosity-average molecular weight of 1000-16000, and moderate viscosity. In the flexible agent's molecular chain, the diisocyanate portion cannot spin due to double bond interaction, acting as a hard segment anchoring group. The diisocyanate is highly polar and can adsorb or embed into the binder molecular chain in the active material layer, enhancing the stretching of the binder molecular chain. The siloxane portion in the flexible agent's molecular chain can rotate freely due to covalent bonds, acting as a soft segment. Furthermore, the siloxane can form strong intermolecular forces with the binder and active material in the active material layer, thereby increasing the dispersibility of the active material and binder and maintaining the stability of the system. Simultaneously, the flexible agent can be uniformly dispersed in the system, reducing strong hydrogen bonding between polymer binder molecules, providing good flexibility for the electrode, thus improving the electrode's flexibility and reducing or avoiding brittle breakage during winding and hot pressing. In addition, the lone pair electrons of the oxygen atoms contained in the flexible agent can coordinate with lithium ions, promote lithium ion transport, reduce battery impedance, and improve the electrochemical performance of the battery.

[0021] In any embodiment, the reaction temperature of the raw materials is 40°C to 70°C, and the reaction time is 4h to 8h.

[0022] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer. The positive electrode film layer is disposed on at least one surface of the positive current collector. The positive electrode film layer includes the flexible agent of the above embodiments or the flexible agent prepared by the preparation method of the flexible agent of the above embodiments.

[0023] Therefore, the positive electrode sheet of this application has good flexibility, reducing or avoiding the phenomenon of brittle breakage of the positive electrode sheet during winding and hot pressing, and the battery made using the positive electrode sheet has good electrochemical performance.

[0024] In any embodiment, the mass percentage of the aforementioned flexible agent in the positive electrode film layer is 0.1 wt% to 0.5 wt%. By keeping the mass percentage of the flexible agent in the positive electrode film layer within this range, the flexible agent can both play a dispersing role and avoid reducing the proportion of positive electrode active material in the positive electrode film layer due to an excessively high proportion, thereby reducing the cell's energy density and kinetic performance. When the mass percentage of the flexible agent in the positive electrode film layer is within the above range, it can improve the flexibility of the positive electrode sheet, reduce or avoid the brittle fracture of the positive electrode sheet during winding and hot pressing, and does not compromise cell performance, resulting in a positive electrode sheet with high cycle performance and rate performance.

[0025] In any embodiment, the positive electrode film layer further includes 89.5 wt% to 99.5 wt% positive electrode active material, 0.3 wt% to 4 wt% conductive agent, 0.5 wt% to 4 wt% first binder, and 0.5 wt% to 2 wt% second binder. By ensuring that the proportions of the positive electrode active material, conductive agent, first binder, and second binder in the positive electrode film layer are within the above ranges, the energy density and dynamic performance of the battery cell can be guaranteed.

[0026] In any embodiment, the first binder includes any one or more of polyvinylidene fluoride, polyvinylidene fluoride-tetrafluoroethylene-propylene terpolymer, polyvinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and fluorinated acrylate resin, and / or the second binder includes any one or more of polytetrafluoroethylene, polychlorotrifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and ethylene-chlorotrifluoroethylene copolymer. The combined use of these two binders satisfies the requirements of the positive electrode sheet manufacturing process, ensuring the positive electrode film has sufficient strength without sticking to the rollers, thus preventing breakage during high-speed belt conveying. Simultaneously, the addition of a flexibility agent to this system improves the flexibility of the positive electrode sheet, reducing or preventing brittle breakage during winding and hot pressing, ensuring good kinetics and cycle performance of the secondary battery.

[0027] The fourth aspect of this application also provides a method for preparing a positive electrode sheet, comprising: first mixing a first binder, an organic solvent and the flexible agent described in the above embodiments to obtain a first mixture; then mixing a positive active material, a conductive agent, a second binder and the first mixture to form a second mixture; then forming the second mixture into a positive electrode film; and finally laminating the positive electrode film onto the surface of a positive current collector and drying it to obtain a positive electrode sheet.

[0028] Therefore, the method for preparing the positive electrode sheet of this application first mixes the flexible agent, the first binder, and the organic solvent in the above embodiments to obtain a uniformly dispersed gel-like first mixture, and then mixes the positive electrode active material, the conductive agent, the second binder, and the first mixture to obtain a clump-like second mixture. The method for preparing the positive electrode sheet of this application is simple, and the obtained positive electrode sheet has good flexibility, reducing or avoiding the phenomenon of brittle breakage of the positive electrode sheet during winding, hot pressing, etc. The battery made using the positive electrode sheet has good electrochemical performance.

[0029] In any embodiment, the solid content of the first mixture is 3% to 20%, and / or the solid content of the second mixture is 70% to 95%. By adding a small amount of solvent during the preparation process to ensure that the solid content of the first and second mixtures are within the above-mentioned ranges, the extruded positive electrode film can be greatly facilitated to particle slippage during the rolling thinning process. The solvent acts like a "lubricant," thus preventing the positive electrode film from being over-rolled, making the positive electrode film more flexible, improving its processing performance, and making it easier to compact the positive electrode sheet and prepare thicker electrodes, thereby achieving high-energy-density batteries. Furthermore, the amount of solvent added in this application is far lower than that in the industry's wet coating process, greatly reducing drying energy consumption and environmental pollution.

[0030] A fifth aspect of this application also provides a battery cell including the positive electrode sheet of the above embodiments.

[0031] A sixth aspect of this application also provides a battery, including the battery cell described in the above embodiments.

[0032] A seventh aspect of this application also provides an electrical device, including a battery cell or battery as described in the above embodiments, wherein the battery cell or battery is used to provide electrical energy.

[0033] This application has at least the following beneficial effects:

[0034] In this application, the diisocyanate portion of the flexible agent's molecular chain cannot spin due to double bond interactions, thus acting as an anchoring group in the hard segment. The diisocyanate is highly polar and can adsorb or embed into the binder molecular chain in the active material layer, enhancing the stretching of the binder molecular chain. The siloxane portion of the flexible agent's molecular chain can rotate freely due to covalent bonds, acting as a soft segment. Furthermore, the siloxane can form strong intermolecular forces with the binder and active material in the active material layer, thereby increasing the dispersibility of the active material and binder and maintaining the stability of the system. Simultaneously, the flexible agent can be uniformly dispersed in the system, reducing strong hydrogen bonding between polymer binder molecules, providing good flexibility for the electrode, and thus improving the electrode's flexibility, reducing or avoiding brittle breakage of the electrode during winding and hot pressing.

[0035] The flexible agent of this application can effectively improve the flexibility of the electrode with a small amount added without affecting the energy density of the battery. In addition, the lone pair electrons of the oxygen atoms contained in the flexible agent can coordinate with lithium ions, promote lithium ion transport, reduce battery impedance, and improve the electrochemical performance of the battery. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0037] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0038] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0039] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0040] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0041] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0042] Figure 7 This is the infrared spectrum of the flexible agent prepared in Example 1 of this application.

[0043] Figure 8 These are comparison images of the cracking of the positive electrode sheet in Embodiment 1 and Comparative Example 1 of this application.

[0044] Explanation of reference numerals in the attached figures:

[0045] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0046] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the flexible agent and its preparation method, the positive electrode sheet and its preparation method, the battery cell, the battery, and the electrical device thereof. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] 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 expected that ranges of 60-110 and 80-120 are also included. 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 "ab" 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.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0050] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] In the electrode preparation process, the electrode is usually prepared by a winding process. However, under the condition of thick coating and high pressure density, the inner corner of the winding is prone to breakage during the hot pressing process, which leads to a decrease in cell performance.

[0052] Based on this, the first aspect of the present application provides a flexibility agent comprising a compound having the following structural formula:

[0053]

[0054] R1 is selected from C 2～10 straight-chain alkylene or Among them, R3, R4, R5, and R6 are all independently selected from H and C. 2～8 ester group, C 2～8 sulfonate group, C 2～8 sulfonates, C 2～8 The amide group or -(CH2-CH2-O)n1-, where n1 is 3 to 6; R2 includes Si-O-Si groups, where x is 3 to 70.

[0055] Straight-chain alkylene groups are hydrocarbon groups derived from straight-chain alkyl groups by removing one hydrogen atom, forming a group with two monovalent groups at its center. For example, C 2～10 A straight-chain alkylene group refers to a hydrocarbon group with two monovalent groups derived from a straight-chain alkyl group by removing one hydrogen atom, which has a total of 2 to 10 carbon atoms.

[0056] Ester group refers to R 13 For example, C is a non-hydrogen group. 2～8 An ester group refers to an ester group with a total of 2 to 8 carbon atoms and containing Organic groups.

[0057] Sulfonate group refers to R 14 For example, C is a non-hydrogen group. 2～8 Sulfonate groups refer to compounds with a total of 2 to 8 carbon atoms and containing Organic groups.

[0058] Sulfonates refer to M includes lithium or sodium, for example, C 2～8 Sulfonates refer to salts with a total of 2 to 8 carbon atoms and containing Organic groups.

[0059] amide group refers to R 15 and R 16 Each group is independently selected from hydrogen or non-hydrogen groups, for example, C 2～8 The amide group refers to a group with a total of 2 to 8 carbon atoms and containing Organic groups.

[0060] -(CH2-CH2-O)n1- refers to a group having 3 to 6 repeating -CH2-CH2-O- structures. For example, -(CH2-CH2-O)n1- can be -(CH2-CH2-O)3-, -(CH2-CH2-O)4-, -(CH2-CH2-O)5-, or -(CH2-CH2-O)6-.

[0061] In this application, the diisocyanate portion of the flexible agent's molecular chain cannot spin due to double bond interactions, thus acting as an anchoring group in the hard segment. The diisocyanate is highly polar and can adsorb or embed into the binder molecular chain in the active material layer, enhancing the stretching of the binder molecular chain. The siloxane portion of the flexible agent's molecular chain can rotate freely due to covalent bonds, acting as a soft segment. Furthermore, the siloxane can form strong intermolecular forces with the binder and active material in the active material layer, thereby increasing the dispersibility of the active material and binder and maintaining the stability of the system. Simultaneously, the flexible agent can be uniformly dispersed in the system, reducing strong hydrogen bonding between polymer binder molecules, providing good flexibility for the electrode, and thus improving the electrode's flexibility, reducing or avoiding brittle breakage of the electrode during winding and hot pressing.

[0062] The flexible agent of this application can effectively improve the flexibility of the electrode with a small amount added without affecting the energy density of the battery. In addition, the lone pair electrons of the oxygen atoms contained in the flexible agent can coordinate with lithium ions, promote lithium ion transport, reduce battery impedance, and improve the electrochemical performance of the battery.

[0063] In some embodiments, the Si-O-Si groups in R2 are located at the ends and / or in the chain. When the Si-O-Si groups in R2 are located in the chain, R2 has no side groups or the number of carbon atoms in the side groups is 1 to 5.

[0064] When the Si-O-Si group in R2 is located at the end, the Si-O-Si group is generally located at the end of the side chain of R2;

[0065] When the Si-O-Si group in R2 is located in the chain, the Si-O-Si group can be located in the main chain of R2 or in the side chain of R2.

[0066] By placing the Si-O-Si groups in R2 at the ends, the siloxane can rotate freely, thereby improving the flexibility of the electrode and reducing or avoiding the brittle fracture of the electrode during winding and hot pressing. Furthermore, by placing the Si-O-Si groups in R2 in the middle of the chain, and by having no side groups or side groups with 1 to 5 carbon atoms, the rotational resistance of the siloxane is low, allowing it to rotate freely, thus improving the flexibility of the electrode and reducing or avoiding the brittle fracture of the electrode during winding and hot pressing.

[0067] In some implementations, R2 includes any of the following structures:

[0068]

[0069] Where a is 13–30, b is 2–10, c is 2–20, d is 2–20, and e is 10–50; R7 is selected from C. 2～12 Straight-chain alkylene groups or -(CH2-CH2-O)n2-, where n2 is 2 to 6; R8 and R9 are each independently selected from C 1～5 Alkyl group; R 10 Selected from C 1～5 Alkyl, C 1～5 Alkoxy, C 1～5 alkylthio or C 1～5 Siloxane; R 11 Selected from C 1～5 Alkyl, C 1～5 Alkoxy or C 1～5 Alkylthio; R 12 Selected from C that has been substituted with one or more hydroxyl groups 2～5 alkyl.

[0070] As an example, the value of a can be 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30.

[0071] Optionally, a can be 14 to 25.

[0072] As an example, the value of b can be 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0073] Optionally, b can be 4 to 8.

[0074] As an example, the value of c can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20.

[0075] Optionally, c can be 3 to 10.

[0076] As an example, the value of d can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20.

[0077] Optionally, d can be 4 to 15.

[0078] As an example, the value of e can be 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48 or 50.

[0079] Optionally, 12–20.

[0080] C 2～12 A straight-chain alkylene group refers to a hydrocarbon group with two monovalent groups derived from a straight-chain alkyl group by removing one hydrogen atom, which has a total of 2 to 12 carbon atoms.

[0081] -(CH2-CH2-O)n2- has 2 to 6 repeating -CH2-CH2-O- groups, for example, -(CH2-CH2-O)n2- can be -(CH2-CH2-O)2-, -(CH2-CH2-O)3-, -(CH2-CH2-O)4-, -(CH2-CH2-O)5- or -(CH2-CH2-O)6-.

[0082] Alkyl groups are straight-chain or branched hydrocarbon chain groups consisting only of carbon and hydrogen atoms, for example, C 1～5 Alkyl groups are straight-chain or branched hydrocarbon groups consisting of 1 to 5 carbon atoms and only carbon and hydrogen atoms.

[0083] Alkoxy refers to -R 17 -O-,R 17 It is an alkyl group, for example, C 1～5 Alkoxy groups are those with a total of 1 to 5 carbon atoms and containing -R. 17 -O- organic groups.

[0084] Alkyl thio group refers to -R 18 -S-,R 18 It is an alkyl group, for example, C 1～5 Alkylthio groups refer to groups with a total of 1 to 5 carbon atoms and containing -R. 18 -S- organic groups.

[0085] C 1～5 Siloxane refers to alkyl groups with a total of 1 to 5 carbon atoms and containing -Si-O- groups.

[0086] C substituted with one or more hydroxyl groups 2～5Alkyl refers to C 2～5 The alkyl group has one or more H atoms that are replaced by OH atoms, forming one or more -OH reaction sites.

[0087] By selecting the above structure for R2, the rotational resistance of the siloxane is smaller, allowing it to rotate freely, thereby improving the flexibility of the electrode and reducing or avoiding the phenomenon of brittle breakage of the electrode during winding and hot pressing.

[0088] In some implementations, R 10 Selected from -CH2Si(OCH3)3, -CH2CH2Si(OCH3)3, -CH2CH2CH2Si(OCH3)3, -(CH2)4Si(OCH3)3, -(CH2)5Si(OCH3)3, -CH2Si(OCH2CH3)3, -(CH2)2Si(OCH2CH3)3, -(CH2)3Si(OCH2CH3)3, -CH2OCH2Si(OCH3)3, -CH2O(CH2)2Si(OCH3)3, -CH2O(CH2)2Si(OCH3)3 or -CH2O(CH2)3Si(OCH3)3.

[0089] In some implementations, R 12 Selected from -CH(CH2OH)CH2CH2OH, -CH(CH2OH)CH2CH2CH2OH or -CH(CH2CH2OH)CH2CH2OH.

[0090] In some embodiments, R3, R4, R5, and R6 are each independently selected from -COOCH3, -COOCH2CH3, -COO(CH2)2CH3, -COO(CH2)3CH3, -COO(CH2)4CH3, -CH2COOCH2CH3, -CH2COO(CH2)2CH3, -CH2COO(CH2)3CH3, -(CH2)2COO(CH2)3CH3, -SO3CH3, -SO3CH2CH3, -SO3(CH2)2CH3, -SO3(CH2)3CH3, -SO3(CH2)4CH3, -CH2SO3CH2CH3, -CH2SO3(CH2)2CH3, -CH2SO3(CH2)3CH3, -(CH2)2SO3CH2CH3, -(CH2)2SO3(CH2)2CH3, -S O2CH3, -SO2CH2CH3, -SO2(CH2)2CH3, -SO2(CH2)3CH3, -SO2(CH2)4CH3, -CH2SO2CH2CH3, -CH2SO 2(CH2)2CH3, -CH2SO2(CH2)3CH3, -(CH2)2SO2CH3, -(CH2)2SO2CH2CH3, -(CH2)2SO2(CH2)2CH3, - SO3A, -CONHCH3, -CONHCH2CH3, -CONH(CH2)2CH3, -CONH(CH2)3CH3, -CONH(CH2)4CH3, -CH2CONHCH2CH3, -CH2CONH(CH2)2CH3, -CH2CONH(CH2)3CH3 or -(CH2)2CONH(CH2)3CH3, where A includes Li, Na, K, or Mg.

[0091] In some implementations, R3, R4, R5, and R6 are not all H at the same time.

[0092] When R3, R4, R5, and R6 are all H, It is -CH2-CH2-. That is, R1 does not include the -CH2-CH2- structure.

[0093] As an example, R3, R4, R5, and R6 can all be non-H, or R3, R4, and R5 can be H but R6 can be non-H, or R3, R4, and R6 can be H but R5 can be non-H, or R3, R5, and R6 can be H but R4 can be non-H, or R4, R5, and R6 can be H but R3 can be non-H, or R3 and R4 can be H but R5 and R6 can be non-H, or R5 and R6 can be H but R3 and R4 can be non-H, or R4 and R5 can be H but R3 and R6 can be non-H, or R3 and R6 can be H but R4 and R5 can be non-H, or R6 can be H but R3, R4, and R5 can be non-H, or R5 can be H but R3, R4, and R6 can be non-H, or R4 can be H but R3, R5, and R6 can be non-H, or R3 can be H but R4, R5, and R6 can be non-H.

[0094] By making R3, R4, R5, and R6 not all simultaneously H, at least one of R3, R4, R5, and R6 is selected from C. 2～8 ester group, C 2～8 sulfonate group, C 2～8 sulfonates, C 2～8 The amide group or -(CH2-CH2-O)n1-, where n1 is 3 to 6, wherein the ester group increases the affinity with the electrolyte and increases the electrolyte wetting rate, while the sulfonate group, sulfonate, amide group and ether can provide lithium ion channels, promote lithium ion transport, and thus improve battery kinetics.

[0095] In some embodiments, the viscosity-average molecular weight of the flexible agent is 1,000 to 16,000.

[0096] As an example, the viscosity-average molecular weight of the flexibility agent can be 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000 or 16000.

[0097] Optionally, the viscosity-average molecular weight of the flexible agent is 5,000 to 16,000.

[0098] Optionally, the viscosity-average molecular weight of the flexible agent is 7,000 to 13,000.

[0099] Viscosity-average molecular weight (VMA) is the molecular weight of a polymer determined by the dilute solution viscometry method. This method is suitable for polymers with a wide molecular weight range, requires simple equipment, is easy to operate, and has high experimental accuracy. The determination of VMA not only provides information on the average molecular weight of the polymer but also yields the unperturbed chain size and expansion factor, making it widely applicable.

[0100] Viscosity-average molecular weight can be determined using the following methods:

[0101] The viscosity-average molecular weight (MAM) of the modified polyacrylic acid binder in liquid phase was determined using gel permeation chromatography (GPC). Specifically, the modified polyacrylic acid binder was diluted with tetrahydrofuran (TFH) to a solid content of 2%, and then injected at a flow rate of 2 mL / min and a pressure of 1250 psi to determine the MAM. A porous gel was used as the stationary phase, and separation was achieved based on the different flow rates of solute molecules of different molecular weights through the gel. Testing instrument: Waters E2695.

[0102] By ensuring the viscosity-average molecular weight of the flexible agent falls within the aforementioned range, it achieves dispersion with a small addition amount without affecting battery energy density, while maintaining low viscosity and good reactivity, and essentially without impacting lithium-ion migration kinetics in the electrode. Flexible agents with a viscosity-average molecular weight of 1000–16000 can effectively improve electrode flexibility and battery electrochemical performance.

[0103] The second aspect of this application provides a method for preparing a flexible agent, which includes reacting raw materials comprising diisocyanate, siloxane-containing diol, solvent and catalyst.

[0104] The diisocyanate has the structural formula OCN-R1-NCO, where R1 is selected from C. 2～10 straight-chain alkylene or Among them, R3, R4, R5, and R6 are all independently selected from H and C. 2～8 ester group, C 2～8 sulfonate group, C 2～8 sulfonates, C 2～8 The amide group or -(CH2-CH2-O)n1-, where n1 is 3 to 6.

[0105] The structural formula of a diol containing siloxane is HO-R2-OH, where R2 includes a Si-O-Si group.

[0106] Solvents include tetrahydrofuran.

[0107] The catalyst includes dibutyltin dilaurate.

[0108] The synthesis method of this application is simple, and the synthesized flexible agent has a stable structure with a viscosity-average molecular weight of 1000-16000 and moderate viscosity. In the flexible agent's molecular chain, the diisocyanate portion, due to double bond interaction, cannot spin and acts as an anchoring group in the hard segment. The diisocyanate is highly polar and can adsorb or embed into the binder molecular chain in the active material layer, enhancing the stretching of the binder molecular chain. The siloxane portion in the flexible agent's molecular chain, due to covalent bonds, can rotate freely and acts as a soft segment. Furthermore, the siloxane can form strong intermolecular forces with the binder and active material in the active material layer, thereby increasing the dispersibility of the active material and binder and maintaining the stability of the system. Simultaneously, the flexible agent can be uniformly dispersed in the system, reducing the strong hydrogen bonding between polymer binder molecules, providing good flexibility for the electrode, and thus improving the electrode's flexibility, reducing or avoiding brittle breakage of the electrode during winding and hot pressing. In addition, the lone pair electrons of the oxygen atoms contained in the flexible agent can coordinate with lithium ions, promote lithium ion transport, reduce battery impedance, and improve the electrochemical performance of the battery.

[0109] In some embodiments, the reaction temperature of the raw materials is 40°C to 70°C, and the reaction time is 4h to 8h.

[0110] As an example, the reaction temperature of the raw materials can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, or 70°C.

[0111] The reaction time of the raw materials can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h.

[0112] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer. The positive electrode film layer is disposed on at least one surface of the positive current collector. The positive electrode film layer includes the flexible agent of the above embodiments or the flexible agent prepared by the preparation method of the flexible agent of the above embodiments.

[0113] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0114] 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.).

[0115] The positive electrode film includes the positive electrode active material.

[0116] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0117] In some embodiments, to further improve the energy density of secondary batteries, the positive electrode active material for lithium-ion batteries may include materials with the general formula Li. a Ni b Coc M d O e A f One or more of lithium transition metal oxides and their modified compounds thereof. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0118] In some embodiments, by way of example, the positive electrode active material for a lithium ion battery may include one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4 and LiMnPO4.

[0119] In some embodiments, when the secondary battery is a sodium ion battery, the positive electrode active material may adopt the positive electrode active material for sodium ion batteries well-known in the art. By way of example, the positive electrode active material may be used alone or in combination of two or more. Among them, the positive electrode active substance may be selected from sodium iron composite oxide (NaFeO2), sodium cobalt composite oxide (NaCoO2), sodium chromium composite oxide (NaCrO2), sodium manganese composite oxide (NaMnO2), sodium nickel composite oxide (NaNiO2), sodium nickel titanium composite oxide (NaNi 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O2), sodium iron manganese composite oxide (Na 2 / 3 Fe<000013O>Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi 1 / 3 Co 1 / 3 Mn 1 / 3O2), sodium iron phosphate (NaFePO4), sodium manganese phosphate (NaMn) P The present application may use materials such as O4, sodium cobalt phosphate (NaCoPO4), Prussian blue materials, and polyanionic materials (phosphates, fluorophosphates, pyrophosphates, sulfates), but this application is not limited to these materials. Other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0120] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0121] As an optional technical approach in this application, the polyanionic compound can be Li 1+x Mn 1-y A y P 1-z R z O4; where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N.

[0122] As an optional technical approach in this application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0123] As an optional technical approach in this application, the polyanionic compound can be Na... 4+x R 3-y P 4-m O 15 / C; where 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0124] As an optional technical solution of the present application, the polyanionic compound can be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d , where the A element represents an alkali metal element that dopes and replaces the Na element, the M element represents a metal element that replaces the V element, the D element represents a doping element that replaces the P element, the Q element represents a doping element that replaces the F element, the D element includes at least one of Si and S, the Q element includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0 ≤ c ≤ 0.15, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, the A element includes at least one of K and Li; the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0125] As an optional technical solution of the present application, when the secondary battery is a sodium-ion battery, the positive electrode active material in the positive electrode active substance can include at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventionally well-known materials that can be used as positive electrode active materials for sodium-ion batteries can also be used.

[0126] In some embodiments, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2, where M is one or several of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1.

[0127] In some embodiments, the polyanionic compound can be a class of compounds having sodium ions, transition metal ions, and tetrahedral (YO4) n- anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4)n- The price state.

[0128] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0129] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, n represents the valence state of V; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0130] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0131] Prussian blue compounds can contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0132] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of cathode materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0133] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0134] In some embodiments, the average particle size Dv50 of the positive electrode active material is 1 μm to 10 μm.

[0135] In some embodiments, the specific surface area of ​​the positive electrode active material is ≤15m². 2 / g.

[0136] 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.

[0137] The positive electrode sheet of this application has good flexibility, which reduces or avoids the phenomenon of brittle breakage of the positive electrode sheet during winding and hot pressing. The battery made using the positive electrode sheet has good electrochemical performance.

[0138] In some embodiments, the mass percentage of the flexible agent in the positive electrode film layer is 0.1 wt% to 0.5 wt%.

[0139] As an example, the mass percentage of the flexible agent in the positive electrode film layer can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%.

[0140] Optionally, the mass percentage of the flexible agent in the positive electrode film layer is 0.2 wt% to 0.3 wt%.

[0141] By ensuring the mass percentage of the flexible agent in the positive electrode film is within the aforementioned range, the flexible agent can effectively disperse the charge without reducing the proportion of positive active material in the film, thus preventing a decrease in cell energy density and kinetic performance. When the mass percentage of the flexible agent in the positive electrode film is within this range, it improves the flexibility of the positive electrode sheet, reducing or preventing brittle fracture during winding and hot pressing, without compromising cell performance. This results in a positive electrode sheet with high cycle performance and rate capability.

[0142] In some embodiments, the positive electrode film layer further includes 89.5 wt% to 99.5 wt% of positive electrode active material, 0.3 wt% to 4 wt% of conductive agent, 0.5 wt% to 4 wt% of first binder and 0.5 wt% to 2 wt% of second binder.

[0143] As an example, the mass percentage of the positive electrode active material in the positive electrode film layer can be 89.5 wt%, 90 wt%, 90.5 wt%, 91 wt%, 91.5 wt%, 92 wt%, 92.5 wt%, 93 wt%, 93.5 wt%, 94 wt%, 94.5 wt%, 95 wt%, 95.5 wt%, 96 wt%, 96.5 wt%, 97 wt%, 97.5 wt%, 98 wt%, 98.5 wt%, 99 wt%, or 99.5 wt%.

[0144] As an example, the mass percentage of the conductive agent in the positive electrode film can be 0.3wt%, 0.4wt%, 0.5wt%, 0.8wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, or 4wt%.

[0145] As an example, the mass percentage of the first binder in the positive electrode film layer can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, or 4wt%.

[0146] As an example, the mass percentage of the second binder in the positive electrode film layer can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, or 2 wt%.

[0147] By ensuring that the proportions of the positive electrode active material, conductive agent, first binder, and second binder in the positive electrode film layer are within the aforementioned range, the energy density and dynamic performance of the battery cell can be guaranteed.

[0148] In some embodiments, the first binder includes any one or more of polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and fluorinated acrylate resin, and / or the second binder includes any one or more of polytetrafluoroethylene, polychlorotrifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and ethylene-chlorotrifluoroethylene copolymer.

[0149] As an example, the first adhesive may be a single polyvinylidene fluoride, a polyvinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a polyvinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, or a fluorinated acrylate resin, or a mixture of any two or three of the above adhesives.

[0150] The second binder may be polytetrafluoroethylene, polychlorotrifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or ethylene-chlorotrifluoroethylene copolymer, or a mixture of any two or three of the above binders.

[0151] The combined use of the two binders described above can meet the requirements of the positive electrode sheet manufacturing process, ensuring that the positive electrode sheet has a certain strength without sticking to the rollers, thus preventing breakage during high-speed conveyor belt operation. Simultaneously, the addition of a flexibility agent to this system can improve the flexibility of the positive electrode sheet, reducing or preventing brittle breakage during winding and hot pressing, thereby ensuring good kinetics and cycle performance of the secondary battery.

[0152] In some embodiments, the second binder has a weight-average molecular weight ≥ 10 million and a relative standard density of 2.10 to 2.19.

[0153] The fourth aspect of this application provides a method for preparing a positive electrode sheet, which includes: first mixing a first binder, an organic solvent and the flexible agent described in the above embodiment to obtain a first mixture; then mixing a positive active material, a conductive agent, a second binder and the first mixture to form a second mixture; then forming a positive electrode film from the second mixture; and finally laminating the positive electrode film onto the surface of a positive current collector and drying it to obtain a positive electrode sheet.

[0154] Optionally, the first mixture is in the form of a gel.

[0155] Alternatively, the method of mixing to form the second mixture includes kneading.

[0156] Optionally, the second mixture is in the form of lumps.

[0157] Alternatively, the second mixture may be formed into a positive electrode membrane by extrusion or hot pressing.

[0158] Optionally, before bonding the positive electrode membrane to the surface of the positive electrode current collector, the positive electrode membrane is thinned, and the method of thinning the positive electrode membrane includes rolling.

[0159] The mixing equipment for the second mixture includes an internal mixer, a kneader, or a twin-screw extruder. The positive electrode film can be formed using a screw extruder, a hydraulic extruder, a plunger extruder, a hot press, or an open mill. The threaded element of the twin-screw extruder can be a combination of one or more of threaded components, meshing blocks, and toothed discs to fully balance shear mixing and conveying capacity.

[0160] The method for preparing the positive electrode sheet of this application involves first mixing the flexible agent, the first binder, and the organic solvent from the above embodiments to obtain a uniformly dispersed gel-like first mixture. Then, mixing the positive electrode active material, the conductive agent, the second binder, and the first mixture facilitates the preparation of a granular second mixture. The method for preparing the positive electrode sheet of this application is simple, and the resulting positive electrode sheet exhibits good flexibility, reducing or avoiding brittle breakage during winding and hot pressing. Batteries made using this positive electrode sheet demonstrate good electrochemical performance.

[0161] In some embodiments, the solid content of the first mixture is 3% to 20%, and / or the solid content of the second mixture is 70% to 95%.

[0162] As an example, the solid content of the first mixture can be 3%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%.

[0163] The solid content of the second mixture can be 70%, 75%, 80%, 85%, 90%, or 95%.

[0164] By adding a small amount of solvent during the preparation process to ensure that the solid content of the first mixture and the solid content of the second mixture are within the aforementioned range, the extruded positive electrode film can be greatly facilitated to particle slippage during the rolling thinning process. The solvent acts like a "lubricant," thus preventing the positive electrode film from being over-rolled, making the positive electrode film more flexible, improving its processing performance, and making it easier to compact the positive electrode sheet and prepare thicker electrodes, thereby achieving high-energy-density batteries. Furthermore, the amount of solvent added in this application is far lower than that in the industry's wet coating process, greatly reducing drying energy consumption and environmental pollution.

[0165] In addition, the battery cell, battery and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0166] [Rechargeable Battery]

[0167] The second aspect of this application provides a secondary battery. This application does not particularly limit the type of secondary battery; for example, the secondary battery can be a lithium-ion battery, etc.

[0168] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0169] This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). This applies to secondary batteries using electrolyte solutions, as well as some secondary batteries using solid electrolytes.

[0170] [Negative electrode plate]

[0171] In some embodiments, 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.

[0172] 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.

[0173] 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.).

[0174] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, 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.

[0175] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from 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).

[0176] In some embodiments, the negative electrode film may optionally include a conductive agent. 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.

[0177] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0178] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the 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 the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0179] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, and may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector.

[0180] In some embodiments, the film layer may further include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0181] [Electrolytes]

[0182] 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.

[0183] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] [Isolation membrane]

[0188] In some embodiments, the secondary battery also 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.

[0189] 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.

[0190] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0191] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0192] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0193] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0194] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0195] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0196] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0197] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0198] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0199] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0200] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0201] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0202] Figure 6This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0203] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0204] Example

[0205] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0206] Example 1

[0207] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0208] S1. Preparation of diols containing siloxanes

[0209] Hydrogen-terminated silicone oil and allyl alcohol were mixed and stirred, and the mixture was heated to 120°C. After the temperature stabilized, chloroplatinic acid catalyst was added dropwise to the system, and the reaction was maintained at this temperature for 4 hours. The hydroxyl-terminated polysiloxane diol was then obtained by vacuum distillation. The molar ratio of hydrogen-terminated silicone oil to allyl alcohol was 1:2.2, and the catalyst dosage was 2 g / kg.

[0210] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0211] S2, Preparation of flexible agent

[0212]

[0213] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reaction vessel. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 50°C for 5 hours under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0214] The structural formula of diisocyanate is as follows:

[0215]

[0216] The viscosity-average molecular weight of the flexibility agent is 6000, and its structural formula is as follows:

[0217]

[0218] The infrared spectrum of the prepared flexible agent is as follows: Figure 7 As shown, 1020cm -1 The stretching vibration peak at 1679 cm⁻¹ is the -CN- peak. -1 The peak is the stretching vibration peak of the C=O ester group, 803 cm⁻¹. -1 The absorption peak at that point is the stretching vibration peak of Si─O─Si.

[0219] S3. Preparation of the positive electrode sheet

[0220] First, polyvinylidene fluoride (PVDF), the prepared flexible agent, and N-methylpyrrolidone (NMP) solvent are mixed to form a first liquid mixture with a solid content of 4.3%. Then, lithium iron phosphate (LFP) positive electrode active material, polytetrafluoroethylene (PTFE) second binder, carbon black (Super P) conductive agent, and the liquid mixture are kneaded together using a kneader to form a second clump mixture with a solid content of 75%. The resulting clump mixture is then extruded using a twin-screw extruder to obtain a positive electrode film of uniform thickness. The prepared positive electrode film is then thinned by rolling to obtain a flexible film, which is then laminated with aluminum foil as a positive electrode current collector. After lamination, the film is dried in an oven, and finally, after further cold pressing and slitting, the positive electrode sheet is obtained. The mass ratio of LFP positive electrode active material, carbon black (Super P) conductive agent, first binder, second binder, and flexible agent is 97.0:0.7:1.8:0.2:0.3.

[0221] Example 2

[0222] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0223] S1. Preparation of diols containing siloxanes

[0224] Hydrogen-terminated silicone oil and allyl alcohol were mixed and stirred, and the mixture was heated to 120°C. After the temperature stabilized, chloroplatinic acid catalyst was added dropwise to the system, and the reaction was maintained at this temperature for 4 hours. The hydroxyl-terminated polysiloxane diol was then obtained by vacuum distillation. The molar ratio of hydrogen-terminated silicone oil to allyl alcohol was 1:2.2, and the catalyst dosage was 2 g / kg.

[0225] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0226]

[0227] S2, Preparation of flexible agent

[0228] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reactor. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 45°C for 5 hours under a nitrogen atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the catalyst weighed 0.5 wt% of the diisocyanate.

[0229] The structural formula of diisocyanate is as follows:

[0230]

[0231] The viscosity-average molecular weight of the flexibility agent is 6500, and its structural formula is as follows:

[0232]

[0233] S3. Preparation of the positive electrode sheet

[0234] Same as Example 1.

[0235] Example 3

[0236] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0237] S1. Preparation of diols containing siloxanes

[0238] Hydrogen-terminated silicone oil and allyl alcohol were mixed and stirred, and the mixture was heated to 120°C. After the temperature stabilized, chloroplatinic acid catalyst was added dropwise to the system, and the reaction was maintained at this temperature for 4 hours. The hydroxyl-terminated polysiloxane diol was then obtained by vacuum distillation. The molar ratio of hydrogen-terminated silicone oil to allyl alcohol was 1:2.2, and the catalyst dosage was 2 g / kg.

[0239] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0240]

[0241] S2, Preparation of flexible agent

[0242] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reaction vessel. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 55°C for 5.5 h under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0243] The structural formula of diisocyanate is as follows:

[0244]

[0245] The viscosity-average molecular weight of the flexibility agent is 7000, and its structural formula is as follows:

[0246]

[0247] S3. Preparation of the positive electrode sheet

[0248] Same as Example 1.

[0249] Example 4

[0250] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0251] S1. Preparation of diols containing siloxanes

[0252] Hydrogen-terminated silicone oil and allyl alcohol were mixed and stirred, and the mixture was heated to 120°C. After the temperature stabilized, chloroplatinic acid catalyst was added dropwise to the system, and the reaction was maintained at this temperature for 4 hours. The hydroxyl-terminated polysiloxane diol was then obtained by vacuum distillation. The molar ratio of hydrogen-terminated silicone oil to allyl alcohol was 1:2.2, and the catalyst dosage was 2 g / kg.

[0253] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0254]

[0255] S2, Preparation of flexible agent

[0256] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reaction vessel. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 60°C for 6 hours under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0257] The structural formula of diisocyanate is as follows:

[0258]

[0259] The viscosity-average molecular weight of the flexibility agent is 8000, and its structural formula is as follows:

[0260]

[0261] S3. Preparation of the positive electrode sheet

[0262] Same as Example 1.

[0263] Example 5

[0264] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0265] S1. Preparation of diols containing siloxanes

[0266] Hydrogen-terminated silicone oil was mixed with CH2=CHOCH2CH2OH and stirred until heated to 125℃. After the temperature stabilized, chloroplatinic acid catalyst was added dropwise to the system, and the reaction was maintained at this temperature for 5 hours. Hydrogen-terminated polysiloxane diol was obtained by vacuum distillation. The molar ratio of hydrogen-terminated silicone oil to allyl alcohol was 1:2.3, and the catalyst dosage was 2 g / kg.

[0267] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0268]

[0269] S2, Preparation of flexible agent

[0270] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reaction vessel. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 50°C for 5 hours under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0271] The structural formula of diisocyanate is as follows:

[0272]

[0273] The viscosity-average molecular weight of the flexibility agent is 7500, and its structural formula is as follows:

[0274]

[0275] S3. Preparation of the positive electrode sheet

[0276] Same as Example 1.

[0277] Example 6

[0278] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0279] S1. Preparation of diols containing siloxanes

[0280] CO2 and propylene oxide were reacted with β-diimine zinc complex at 20 °C and 0.65 MPa for 48 h. The product was then reacted with CH2OCHCH2O(CH2)3Si(OCH3)3 at 130 °C and 0.25 MPa for 24 h with KOH catalysis. The product was then distilled to obtain hydroxyl polysiloxane diol.

[0281] The structural formula of the obtained hydroxyl polysiloxane diol is as follows:

[0282]

[0283] S2, Preparation of flexible agent

[0284] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reactor. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 60°C for 7 hours under a nitrogen atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the catalyst weighed 0.5 wt% of the diisocyanate.

[0285] The structural formula of diisocyanate is as follows:

[0286]

[0287] The viscosity-average molecular weight of the flexibility agent is 9000, and its structural formula is as follows:

[0288]

[0289] S3. Preparation of the positive electrode sheet

[0290] Same as Example 1.

[0291] Example 7

[0292] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0293] S1. Preparation of diols containing siloxanes

[0294] CO2 and CH2OCHCH2OCH2CH3 were reacted with a β-diimine zinc complex at 20 °C and 0.65 MPa for 48 h. The product was then reacted with propylene oxide and CH2OCHCH2O(CH2)3Si(OCH3)3 at 150 °C and 0.25 MPa under KOH catalysis for 28 h. The product was then distilled to obtain hydroxyl polysiloxane diol.

[0295] The structural formula of the obtained hydroxyl polysiloxane diol is as follows:

[0296]

[0297] S2, Preparation of flexible agent

[0298] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reactor. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 60°C for 7 hours under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0299] The structural formula of diisocyanate is as follows:

[0300]

[0301] The viscosity-average molecular weight of the flexibility agent is 12000, and its structural formula is as follows:

[0302]

[0303] S3. Preparation of the positive electrode sheet

[0304] Same as Example 1.

[0305] Example 8

[0306] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0307] S1. Preparation of diols containing siloxanes

[0308] CO2 was reacted with CH2OCHCH2OCHSi(OCH3)3 under the catalysis of β-diimine zinc disulfide at 30 °C and 0.7 MPa for 54 h. The product was then reacted with propylene glycol and CH2OCHCH2O(CH2)3Si(OCH3)3 under the catalysis of KOH at 150 °C and 0.3 MPa for 28 h. After distillation, hydroxyl polysiloxane diol was obtained.

[0309] The structural formula of the obtained hydroxyl polysiloxane diol is as follows:

[0310]

[0311] S2, Preparation of flexible agent

[0312] The obtained product, diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reaction vessel. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 50°C for 5.5 hours under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0313] The structural formula of diisocyanate is as follows:

[0314]

[0315] The viscosity-average molecular weight of the flexibility agent is 10,000, and its structural formula is as follows:

[0316]

[0317] S3. Preparation of the positive electrode sheet

[0318] Same as Example 1.

[0319] Example 9

[0320] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0321] S1. Preparation of diols containing siloxanes

[0322] Propylene glycol was reacted with CH2OCHCH2O(CH2)3Si(OCH3)3 under KOH catalysis at 120℃ and 0.3MPa for 20h, and the resulting product was obtained by distillation to obtain hydroxyl-terminated polysiloxane glycol.

[0323] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0324]

[0325] S2, Preparation of flexible agent

[0326] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reaction vessel. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 50°C for 5 hours under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0327] The structural formula of diisocyanate is as follows:

[0328]

[0329] The viscosity-average molecular weight of the flexibility agent is 9000, and its structural formula is as follows:

[0330]

[0331] S3. Preparation of the positive electrode sheet

[0332] Same as Example 1.

[0333] Example 10

[0334] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0335] S1. Preparation of diols containing siloxanes

[0336] Pentamethyldisiloxane and 1,4-dihydroxy-2-butene were reacted by adding chloroplatinic acid catalyst dropwise to the system at 120°C and maintaining the temperature for 5 hours. The reaction was then carried out by vacuum distillation to obtain hydroxyl-terminated polysiloxane diol. The molar ratio of pentamethyldisiloxane to 1,4-dihydroxy-2-butene was 1:2, and the catalyst dosage was 2 g / kg.

[0337] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0338]

[0339] S2, Preparation of flexible agent

[0340] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reactor. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 40°C for 3.5 hours under a nitrogen atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the catalyst weighed 0.5 wt% of the diisocyanate.

[0341] The structural formula of diisocyanate is as follows:

[0342]

[0343] The viscosity-average molecular weight of the flexibility agent is 9500, and its structural formula is as follows:

[0344]

[0345] S3. Preparation of the positive electrode sheet

[0346] Same as Example 1.

[0347] Example 11

[0348] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0349] S1. Preparation of diols containing siloxanes

[0350] Pentamethyldisiloxane and 1,6-dihydroxy-3-butene were reacted by adding chloroplatinic acid catalyst dropwise to the system at 120°C and maintaining the temperature for 5 hours. The reaction was then carried out by vacuum distillation to obtain hydroxyl-terminated polysiloxane diol. The molar ratio of pentamethyldisiloxane to 1,4-dihydroxy-2-butene was 1:2, and the catalyst dosage was 2 g / kg.

[0351] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0352]

[0353] S2, Preparation of flexible agent

[0354] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reactor. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 40°C for 3.5 hours under a nitrogen atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the catalyst weighed 0.5 wt% of the diisocyanate.

[0355] The structural formula of diisocyanate is as follows:

[0356]

[0357] The viscosity-average molecular weight of the flexibility agent is 8500, and its structural formula is as follows:

[0358]

[0359] S3. Preparation of the positive electrode sheet

[0360] Same as Example 1.

[0361] Example 12

[0362] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0363] S1. Preparation of diols containing siloxanes

[0364] Pentamethyldisiloxane and 1,6-dihydroxy-3-butene were reacted by adding chloroplatinic acid catalyst dropwise to the system at 120°C and maintaining the temperature for 5 hours. The reaction was then carried out by vacuum distillation to obtain hydroxyl-terminated polysiloxane diol. The molar ratio of pentamethyldisiloxane to 1,4-dihydroxy-2-butene was 1:2, and the catalyst dosage was 2 g / kg.

[0365] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0366]

[0367] S2, Preparation of flexible agent

[0368] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reaction vessel. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 40°C for 1.5 h under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0369] The structural formula of diisocyanate is as follows:

[0370]

[0371] The viscosity-average molecular weight of the flexibility agent is 1500, and its structural formula is as follows:

[0372]

[0373] S3. Preparation of the positive electrode sheet

[0374] Same as Example 1.

[0375] Example 13

[0376] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method, which includes the following steps:

[0377] S1. Preparation of diols containing siloxanes

[0378] Pentamethyldisiloxane and 1,6-dihydroxy-3-butene were reacted by adding chloroplatinic acid catalyst dropwise to the system at 120°C and maintaining the temperature for 5 hours. The reaction was then carried out by vacuum distillation to obtain hydroxyl-terminated polysiloxane diol. The molar ratio of pentamethyldisiloxane to 1,4-dihydroxy-2-butene was 1:2, and the catalyst dosage was 2 g / kg.

[0379] The structural formula of the obtained hydroxyl-terminated polysiloxane diol is as follows:

[0380]

[0381] S2, Preparation of flexible agent

[0382] The obtained hydroxyl-terminated polysiloxane diol, diisocyanate, and catalyst dibutyltin dilaurate were added to a reaction vessel. Tetrahydrofuran was used as the solvent, and the reaction was carried out at 40°C for 6 hours under a N2 atmosphere to obtain the flexible agent. The molar ratio of hydroxyl-terminated polysiloxane diol to diisocyanate was 1:1, and the weight of the catalyst was 0.5 wt% of the weight of diisocyanate.

[0383] The structural formula of diisocyanate is as follows:

[0384]

[0385] The viscosity-average molecular weight of the flexibility agent is 16,000, and its structural formula is as follows:

[0386]

[0387] S3. Preparation of the positive electrode sheet

[0388] Same as Example 1.

[0389] Example 14

[0390] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method. The mass ratio of the positive electrode active material lithium iron phosphate, the conductive agent carbon black (Super P), the first binder, the second binder, and the flexible agent is 97.2:0.7:1.8:0.2:0.1, and the rest is the same as in Example 5.

[0391] Example 15

[0392] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method. The mass ratio of the positive electrode active material lithium iron phosphate, the conductive agent carbon black (Super P), the first binder, the second binder, and the flexible agent is 97.1:0.7:1.8:0.2:0.2, and the rest is the same as in Example 5.

[0393] Example 16

[0394] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method. The mass ratio of the positive electrode active material lithium iron phosphate, the conductive agent carbon black (Super P), the first binder, the second binder, and the flexible agent is 96.9:0.7:1.8:0.2:0.4, and the rest is the same as in Example 5.

[0395] Example 17

[0396] This application provides a flexible agent and its preparation method, as well as a positive electrode sheet and its preparation method. The mass ratio of the positive electrode active material lithium iron phosphate, the conductive agent carbon black (Super P), the first binder, the second binder, and the flexible agent is 96.8:0.7:1.8:0.2:0.5, and the rest is the same as in Example 5.

[0397] Comparative Example 1

[0398] This application provides a positive electrode sheet and its preparation method in a comparative example, which includes the following steps:

[0399] First, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) are mixed to form a gel-like first mixture with a solid content of 4.3%. Then, lithium iron phosphate (LFP) as the positive electrode active material, polytetrafluoroethylene (PTFE) as the second binder, carbon black (Super P) as the conductive agent, and the gel-like mixture are kneaded together using a kneader to form a clump-like second mixture with a solid content of 75%. The clump-like second mixture is then extruded using a twin-screw extruder to obtain a positive electrode film of uniform thickness. The prepared positive electrode film is then thinned by rolling to obtain a flexible film, which is then laminated with aluminum foil as the positive electrode current collector. After lamination, the film is dried in an oven, and finally, after further cold pressing and slitting, the positive electrode sheet is obtained. The mass ratio of LFP, carbon black (Super P), the first binder, and the second binder is 97.3:0.7:1.8:0.2.

[0400] The viscosity-average molecular weight of the flexible agent in this application can be determined using the following method:

[0401] The viscosity-average molecular weight (MAM) of the modified polyacrylic acid binder in liquid phase was determined using gel permeation chromatography (GPC). Specifically, the modified polyacrylic acid binder was diluted with tetrahydrofuran (TFH) to a solid content of 2%, and then injected at a flow rate of 2 mL / min and a pressure of 1250 psi to determine the MAM. A porous gel was used as the stationary phase, and separation was achieved based on the different flow rates of solute molecules of different molecular weights through the gel. Testing instrument: Waters E2695.

[0402] The key parameters of Examples 1-17 and Comparative Example 1 are shown in Tables 1 and 2.

[0403] Table 1: Structural formulas of diisocyanates and siloxane-containing diols from Examples 1-17 and Comparative Example 1

[0404]

[0405]

[0406]

[0407]

[0408] Table 2: Structural formulas, viscosity-average molecular weights, and percentages in the positive electrode sheets of the flexible agents used in Examples 1-17 and Comparative Example 1

[0409]

[0410]

[0411]

[0412]

[0413]

[0414] In addition, the positive electrode sheets obtained in Examples 1-17 and Comparative Example 1 were used to prepare secondary batteries as shown below, and performance tests were conducted. The test results are shown in Table 3 below.

[0415] (1) Preparation of secondary batteries

[0416] S1, Preparation of negative electrode sheet

[0417] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are mixed thoroughly in an appropriate amount of deionized water at a mass ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0418] S2, Preparation of Electrolyte

[0419] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0420] S3. Preparation of the separating membrane

[0421] Porous polyethylene film is used as the separator.

[0422] S4. Battery fabrication

[0423] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping, the battery is obtained.

[0424] (2) DCR (DC internal resistance) performance test

[0425] At 25°C, the battery is charged to 3.65V at a constant current of 0.33C, and then discharged to 0.5Cn (Cn represents the battery capacity) at a constant current of 0.33C. The protection voltage is 2.5V to adjust the battery to 50% SOC. The battery is left to stand for 30 minutes, and the voltage after the standing period is recorded as V1. Then, the battery is discharged at a current of 3C (recorded as I) for 30 seconds, and the discharge cutoff voltage is recorded as V2.

[0426] The DC internal resistance of the battery is DCR = (V1-V2) / I, where V1 represents the resting end voltage, V2 represents the discharge cutoff voltage, and I represents the discharge current.

[0427] (3) Ratio Performance Test

[0428] Rate discharge: Charge at 0.33C to a constant voltage of 3.65V, charge to a current of 0.05C, let stand for 5 minutes, discharge at 0.33C to 2.5V and measure the discharge capacity during this period, let stand for 30 minutes; Charge at 0.33C to a constant voltage of 3.65V, charge to a current of 0.05C, let stand for 5 minutes, discharge at 2C to 2.5V and measure the discharge capacity during this period, let stand for 30 minutes. 2C capacity retention rate = 2C discharge capacity / 0.33C discharge capacity * 100%.

[0429] (4) Cyclic performance test

[0430] At 25°C, the battery was charged at a constant current of 1C to 3.65V, and then charged at a constant voltage until the current was 0.05C. After resting for 30 minutes, the battery was discharged at a constant current of 1C to 2.5V and then rested for 30 minutes. The discharge capacity C0 of the battery was recorded.

[0431] The battery was cycle-tested as follows: At 25°C, the battery was charged at a constant current of 1C0 to 3.65V, then charged at a constant voltage until the current reached 0.05C. After resting for 30 minutes, the battery was discharged at a constant current of 1C0 to 2.5V, and then rested for 30 minutes. The discharge capacity of the battery in the first cycle is C1. The battery was cycle-charged and discharged according to the above method. The discharge capacity of the second cycle is C2, ..., and the discharge capacity of the 1200th cycle is C... n With C n / C1 indicates the battery's cycle performance, C n The larger the / C1 value, the better the battery's cycle performance.

[0432] (5) Positive electrode brittleness test

[0433] Cut the electrode sheet into strips 150mm long and 30mm wide using a custom die; fold it in half and roll it with a 2kg rubber roller, observing the cracking of the electrode sheet. If the electrode sheet is translucent or breaks, record it as one cracking. If it is not translucent, fold it in half again and roll it with a 2kg rubber roller, repeating this process until the electrode sheet is translucent or breaks, and record the number of times.

[0434] Table 3: Performance test results of Examples 1-17 and Comparative Example 1

[0435]

[0436]

[0437] As can be seen from Examples 1 to 17, the DC internal resistance of the positive electrode sheet prepared in the embodiments of this application is 0.62mΩ to 0.71mΩ, the 2C capacity retention rate is 94.5% to 96.1%, the capacity retention rate after 1200 cycles is 82% to 84.6%, and the positive electrode sheet can only transmit light or break after being folded and rolled 2 to 3 times respectively.

[0438] A comparison between Example 12 and Example 10 shows that the viscosity-average molecular weight of the flexible agent synthesized in Example 12 is lower, resulting in a higher DC internal resistance, lower 2C capacity retention, and lower capacity retention after 1200 cycles. The positive electrode sheet will become transparent or break after being folded and rolled twice.

[0439] As can be seen from the comparison between Example 13 and Example 11, the viscosity-average molecular weight of the flexible agent synthesized in Example 13 is higher, the DC internal resistance of the resulting positive electrode sheet is greater, the 2C capacity retention rate is lower, the 1200-cycle capacity retention rate is even lower, and the positive electrode sheet will become transparent or break after being folded in half and rolled twice respectively.

[0440] As can be seen from Examples 5 and 14-17, when the mass percentage of the flexible agent in the positive electrode film layer is 0.1wt% to 0.5wt%, as the mass percentage of the flexible agent in the positive electrode film layer increases, the DC internal resistance of the obtained positive electrode sheet first decreases and then increases, the 2C capacity first increases and then decreases, and the 1200-cycle capacity first increases and then decreases. Furthermore, when the mass percentage of the flexible agent in the positive electrode film layer is 0.2wt% to 0.3wt%, the positive electrode sheet will only become transparent or break after being folded and rolled three times respectively. When the mass percentage of the flexible agent in the positive electrode film layer is 0.1wt% or 0.4wt% to 0.5wt%, the positive electrode sheet will become transparent or break after being folded and rolled twice respectively.

[0441] Comparing Comparative Example 1 with Examples 1-17, it can be seen that the positive electrode sheet of Comparative Example 1 does not contain a flexible agent, resulting in a higher DC internal resistance, lower 2C capacity retention, and even lower capacity retention after 1200 cycles. The positive electrode sheet becomes translucent or breaks after only one fold and roll. A comparison of the cracking of the positive electrode sheets of Example 1 and Comparative Example 1 is shown in the figure. Figure 8 As shown, it can be seen that the positive electrode sheet of Comparative Example 1 has become translucent or broken after being folded and rolled once, while the positive electrode sheet of Example 1 only has one crease and has not become translucent or broken.

[0442] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A flexible agent, characterized in that, The flexible agent includes a compound having the following structural formula: R1is selected from C 2～10 straight-chain alkylene or wherein R3, R4, R5and R6are each independently selected from H, C 2～8 ester, C 2～8 sulfonate, C 2～8 sulfonate, C 2～8 amide or -(CH2-CH2-O)n1-, n1 being 3 to 6; R2 includes a Si—O—Si group; x is 3-70.

2. The flexible agent of claim 1, wherein, The Si—O—Si group in R2 is located at the end and / or in the chain; When the Si—O—Si group in R2 is located in the chain, R2 has no side group or each side group has 1-5 carbons.

3. The flexible agent of claim 1, wherein, R2 includes any one of the following structures: wherein a is 13-30, b is 2-10, c is 2-20, d is 2-20, and e is 10-50; R7is selected from C 2～12 straight-chain alkylene or -(CH2-CH2-O)n2-, n2is 2 to 6; R8and R9are each independently selected from C 1～5 alkyl; R 10 selected from C 1～5 alkyl, C 1～5 alkoxy, C 1～5 alkylthio or C 1～5 siloxane group; R 11 selected from C 1～5 alkyl, C 1～5 alkoxy or C 1～5 alkylthio; R 12 selected from C 2～5 alkyl substituted by one or more hydroxyl groups.

4. The flexible agent of claim 3, wherein, said R 10 is selected from -CH2Si(OCH3)3, -CH2CH2Si(OCH3)3, -CH2CH2CH2Si(OCH3)3, -(CH2)4Si(OCH3)3, -(CH2)5Si(OCH3)3, -CH2Si(OCH2CH3)3, -(CH2)2Si(OCH2CH3)3, -(CH2)3Si(OCH2CH3)3, -CH2OCH2Si(OCH3)3, -CH2O(CH2)2Si(OCH3)3, -CH2O(CH2)2Si(OCH3)3, or -CH2O(CH2)3Si(OCH3)3.

5. The flexible agent according to claim 3 or 4, characterized in that, said R 12 is selected from -CH(CH2OH)CH2CH2OH, -CH(CH2OH)CH2CH2CH2OH, or - CH(CH2CH2OH)CH2CH2OH.

6. The flexibilizer according to any one of claims 1 to 5, characterized in that, R3, R4, R5, and R6 are independently selected from -COOCH3, -COOCH2CH3, -COO(CH2)2CH3, -COO(CH2)3CH3, -COO(CH2)4CH3, -CH2COOCH2CH3, -CH2COO(CH2)2CH3, -CH2COO(CH2)3CH3, -(CH2)2COO(CH2)3CH3, -SO3CH3, -SO3CH2CH3, -SO3(CH2)2CH3, -SO3(CH2)3CH3, -SO3(CH2)4CH3, -CH2SO3CH2CH3, -CH2SO3(CH2)2CH3, -CH2SO3(CH2)3CH3, -(CH2)2SO3CH3, -(CH2)2SO3CH2CH3, -(CH2)2SO3(CH2)2CH3, -SO2CH3, -SO2CH2CH3, -SO2(CH2)2CH3, -SO2(CH2)3CH3, -SO2(CH2)4CH3, -CH2SO2CH2CH3, -CH2SO2(CH2)2CH3, -CH2SO2(CH2)3CH3, -(CH2)2SO2CH3, -(CH2)2SO2CH2CH3, -(CH2)2SO2(CH2)2CH3, -SO3A, -CONHCH3, -CONHCH2CH3, -CONH(CH2)2CH3, -CONH(CH2)3CH3, -CONH(CH2)4CH3, -CH2CONHCH2CH3, -CH2CONH(CH2)2CH3, -CH2CONH(CH2)3CH3, or -(CH2)2CONH(CH2)3CH3, wherein A includes Li, Na, K, or Mg.

7. The flexibilizer according to any one of claims 1 to 6, characterized in that, R3, R4, R5, and R6 are not simultaneously H.

8. The flexibilizer according to any one of claims 1 to 7, characterized in that, The flexible agent has a viscosity average molecular weight of 1000-16000.

9. A method of preparing a flexible agent, characterized by, The method for preparing the flexible agent includes reacting raw materials including diisocyanate, a siloxane group-containing diol, a solvent, and a catalyst; R1is selected from the group consisting of C 2～10 linear alkylene or wherein R3, R4, R5and R6are each independently selected from H, C 2～8 ester group, C 2～8 sulfonate group, C 2～8 sulfonate, C 2～8 amide group or -(CH2-CH2-O)n1-, n1is 3 to 6; The siloxane group-containing diol has a structural formula of HO-R2-OH, and R2 includes a Si—O—Si group.

10. The method for preparing the flexible agent according to claim 9, wherein the raw materials are reacted at a temperature of 40-70°C for 4-8 hours.

11. A positive electrode sheet characterized by comprising: The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer, the positive electrode film layer is arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer comprises the flexible agent of any one of claims 1-8 or the flexible agent prepared by the preparation method of claim 9 or 10.

12. The cathode electrode of claim 11, wherein, The mass percentage of the flexible agent in the positive electrode film layer is 0.1wt%-0.5wt%.

13. The cathode electrode of claim 12, wherein, The positive electrode film layer further comprises 89.5wt%-99.5wt% of a positive electrode active material, 0.3wt%-4wt% of a conductive agent, 0.5wt%-4wt% of a first binder, and 0.5wt%-2wt% of a second binder.

14. The cathode electrode of claim 13, wherein, The first binder comprises any one or more of polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and fluorine-containing acrylic ester resin, and / or The second binder comprises any one or more of polytetrafluoroethylene, polychlorotrifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and ethylene-chlorotrifluoroethylene copolymer.

15. A method of producing the positive electrode sheet according to any one of claims 11 to 14, characterized by, The preparation method of the positive electrode tab comprises: mixing the first binder, the organic solvent, and the flexible agent to obtain a first mixture, mixing the positive electrode active material, the conductive agent, the second binder, and the first mixture to obtain a second mixture, forming the second mixture into a positive electrode film, and then coating the positive electrode film on the surface of the positive electrode current collector to obtain the positive electrode tab.

16. The method of producing a cathode electrode piece according to claim 15, wherein The solid content of the first mixture is 3%-20%, and / or the solid content of the second mixture is 70%-95%.

17. A battery cell, characterized by The battery cell comprises the positive electrode tab of any one of claims 11-14.

18. A battery, characterized by The battery comprises the battery cell of claim 17.

19. An electrical device, comprising: The electrical equipment comprises the battery cell of claim 17 or the battery of claim 18, and the battery cell or the battery is used to provide electrical energy.

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