Thermo-sensitive polymer fiber, preparation method, lithium secondary battery and electric device

Abstract

The invention provides a thermo-sensitive polymer fiber for negative electrode slurry. The thermo-sensitive polymer fiber comprises a renewable biomass fiber and a thermo-sensitive polymer. The invention also provides a preparation method of the thermo-sensitive polymer fiber, a lithium secondary battery containing the thermo-sensitive polymer fiber, and an electric device containing the thermo-sensitive polymer fiber. The thermo-sensitive polymer fiber provided by the invention has the characteristics of excellent thermo-sensitive characteristic, good mechanical property, good thermal stability, easy size adjustment and the like, so that the lithium secondary battery prepared by using the thermo-sensitive polymer fiber provided by the invention as the negative electrode paste has improved performance.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a temperature-sensitive polymer fiber, a preparation method, a lithium secondary battery and an electrical device. Background Art

[0002] In recent years, as the application scope of lithium-ion batteries has become more and more extensive, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As lithium-ion batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance. Summary of the invention

[0003] The purpose of the present application is to provide a temperature-sensitive polymer fiber and a preparation method thereof. The temperature-sensitive polymer fiber can be used in the manufacture of battery negative electrode materials to improve the cycle performance of the battery.

[0004] In order to achieve the above-mentioned object, a first aspect of the present application provides a temperature-sensitive polymer fiber for negative electrode slurry, wherein the temperature-sensitive polymer fiber comprises a renewable biomass fiber and a temperature-sensitive polymer.

[0005] The properties of the thermosensitive polymer fiber depend on the physical properties of the biomass fiber, which has the advantages of good mechanical properties, good thermal stability, and easy-to-adjust size. At the same time, the properties of the thermosensitive polymer fiber also depend on the properties of the thermosensitive polymer, whose own properties can change with temperature, so the switching of the hydrophilic and hydrophobic properties of the fiber surface can be achieved by controlling the external temperature. Therefore, the application field of the thermosensitive polymer fiber provided by the present application is relatively wide, for example, it can be used in battery negative electrode slurry.

[0006] In any embodiment, the renewable biomass fiber includes at least one of cellulose fiber, chitosan fiber, chitin fiber, silk fiber, and animal fiber.

[0007] The renewable biomass fibers selected in this application have the characteristics of wide sources and abundant raw materials, so the temperature-sensitive polymer fibers of this application are easy to mass-produce. At the same time, the renewable biomass fibers selected in this application can impart the physical properties of the fibers themselves to the modified temperature-sensitive polymer fibers, such as good mechanical properties, light weight, liquid retention, low linear thermal expansion coefficient, good thermal stability, easy-to-adjust aspect ratio, etc., and can prepare temperature-sensitive polymer fibers with a variety of excellent physical properties.

[0008] In any embodiment, the surface of the renewable biomass fiber has chemical groups, and based on the mass of the renewable biomass fiber, the content of the chemical groups is 5 to 10 mmol / g, and can be 10 mmol / g.

[0009] In any embodiment, the chemical group includes at least one of a hydroxyl group, an amine group, an amide group, and an ester group.

[0010] The renewable biomass fibers selected in the present application have a variety of active groups on their surface and have certain solvent resistance properties, so there is a large space for subsequent modification.

[0011] In any embodiment, the thermosensitive polymer includes at least one of poly(N-vinylcaprolactam), poly(N-isopropylacrylamide), poly(N,N-diethylacrylamide), poly(dicarboxyisopropylacrylamide), and poly[2-(N,N-dimethylamino)methacrylate].

[0012] In any embodiment, the weight average molecular weight of the thermosensitive polymer is 5-20w, and can be 10w.

[0013] In the present application, different thermosensitive polymers can be selected to prepare different thermosensitive polymer fibers. Since different thermosensitive polymers have different low melting temperatures, a wider temperature application window can be provided for the application of thermosensitive polymer fibers.

[0014] In any embodiment, the thermosensitive polymer is connected to the surface of the renewable biomass fiber. Optionally, the thermosensitive polymer is connected to the surface of the renewable biomass fiber through a coupling reaction or a polymerization reaction.

[0015] In any embodiment, the coupling reaction or polymerization reaction includes at least one of an amide condensation reaction, a Schiff base reaction, an esterification reaction, and a free radical polymerization reaction.

[0016] Amide condensation, Schiff base, and free radical polymerization reactions are all relatively mature methods of surface grafting modification. The range of condensation agents available is wide, and different condensation agents can be used to graft different reaction raw materials.

[0017] In any embodiment, the renewable biomass fiber has surface amino modification.

[0018] In any embodiment, the surface of the renewable biomass fiber is amino-modified by a silane coupling agent, the silane coupling agent includes at least one of aminopropyltrimethoxysilane and aminopropyltriethoxysilane, and the mass ratio of the silane coupling agent to the renewable biomass fiber is (0.5-1):1, and can be optionally 1:1.

[0019] The selection of silane coupling agents with different end groups can provide sufficient possibilities for the surface modification of renewable biomass fibers and provide sufficient guarantees for the mass production of temperature-sensitive polymer fibers.

[0020] In any embodiment, the thermosensitive polymer has active group end-capping, and the active group end-capping includes at least one of carboxyl end-capping, acyl chloride end-capping, or aldehyde end-capping.

[0021] Similarly, different active groups can be selected to terminate the thermosensitive polymer to adapt to the mass production of thermosensitive polymer fibers.

[0022] In any embodiment, the diameter of the temperature-sensitive polymer fiber is 10 nm to 200 nm, and can be 50 nm to 100 nm.

[0023] In any embodiment, the length of the temperature-sensitive polymer fiber is 0.5 μm to 100 μm, and can be optionally 10 to 50 μm.

[0024] In any embodiment, the aspect ratio of the temperature-sensitive polymer fiber is (20:1) to (2000:1), and can be optionally (200:1) to (800:1).

[0025] In any embodiment, the temperature change range of the temperature-sensitive polymer fiber is 37°C to 40°C, and can be 37°C.

[0026] The temperature-sensitive polymer fiber provided in the present application has excellent properties and can be applied in various fields. For example, by adding the temperature-sensitive fiber with the above-mentioned properties in the preparation process of the negative electrode plate, it can ensure its good dispersion in the slurry at the processing temperature (temperature lower than the low eutectic temperature), and construct a three-dimensional network structure between the active coatings of the plate after coating; during the baking process (temperature higher than the low eutectic temperature), the three-dimensional hydrophobic network formed by it can prevent the capillary force formed in the plate during the evaporation of the solvent, which causes the binder to float up.

[0027] In any embodiment, based on the total mass of the negative electrode slurry, the content of the temperature-sensitive polymer fiber is 0.01 to 3 wt %, and may be 0.1 wt % to 0.5 wt %.

[0028] Adding a certain amount of temperature-sensitive polymer fibers into the negative electrode slurry can ensure the processing properties of the slurry, such as the filterability of the slurry.

[0029] The second aspect of the present application also provides a method for preparing a temperature-sensitive polymer fiber, wherein a temperature-sensitive polymer is connected to the surface of a renewable biomass fiber to obtain the temperature-sensitive polymer fiber.

[0030] In any embodiment, the method comprises the following steps:

[0031] Modifying the surface of the renewable biomass fiber with amino groups by using a silane coupling agent to obtain a renewable biomass fiber with amino groups modified on the surface;

[0032] The thermosensitive polymer is terminated with active groups to obtain an active group-terminated thermosensitive polymer;

[0033] The active group-terminated temperature-sensitive polymer is connected to the surface of the amino-modified renewable biomass fiber to obtain the temperature-sensitive polymer fiber for negative electrode slurry.

[0034] The present application proposes a method for preparing mass-producible thermosensitive polymer fibers, which uses renewable biomass fibers that can be mass-produced at tons level as a substrate, and grafts thermosensitive polymers on the surface through polymerization or coupling reactions. This not only solves the problem that traditional thermosensitive polymer fibers are difficult to mass-produce, but also prepares thermosensitive polymer fibers with excellent thermosensitive properties: when the ambient temperature is lower than the low eutectic temperature, it is hydrophilic; when the ambient temperature is higher than the low eutectic temperature, it is hydrophobic, and has broad application prospects.

[0035] In any embodiment, the thermosensitive polymer is attached to the surface of the renewable biomass fiber through a coupling reaction or a polymerization reaction.

[0036] In any embodiment, the coupling reaction or polymerization reaction includes at least one of an amide condensation reaction, a Schiff base reaction, an esterification reaction, and a free radical polymerization reaction.

[0037] Amide condensation reaction, Schiff base reaction, esterification reaction, and free radical polymerization reaction are all relatively mature methods of surface grafting modification. The range of condensation agents available is wide, and different condensation agents can be used to graft different reaction raw materials.

[0038] A third aspect of the present application provides a lithium secondary battery, the lithium secondary battery comprising a negative electrode slurry, the negative electrode slurry comprising the temperature-sensitive polymer fiber of the first aspect of the present application.

[0039] The advantages of adding temperature-sensitive polymer fibers to the negative electrode slurry are: first, after the slurry on the negative electrode plate dries, an "interlocking" structure is formed between the fiber-graphite / hard carbon / silicon-fiber. This structure not only stabilizes the structure of the plate, but also increases the exposed surface area of ​​graphite / hard carbon / silicon, which is beneficial to the embedding / de-embedding of lithium ions per unit time, improves the anode dynamics and shortens the battery charging time; second, the added temperature-sensitive polymer fibers can adhere to the surface of a single graphite particle, hindering the expansion of graphite due to lithium embedding.

[0040] A fourth aspect of the present application provides an electrical device, which includes the lithium secondary battery of the third aspect of the present application.

[0041] The temperature-sensitive polymer fiber provided in the present application has excellent temperature-sensitive properties, good mechanical properties, good thermal stability, and easily adjustable size, etc. Therefore, the secondary battery made by using the temperature-sensitive polymer fiber provided in the present application as the negative electrode slurry has improved dynamic performance and cycle performance. Correspondingly, the electric device provided in the present application also has good performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The figures are the surface morphology measurement diagrams of the unmodified renewable biomass fiber and the thermosensitive polymer fiber prepared in Example 1. Among them, a1) is the SEM image (5000 times) of the initial renewable biomass fiber; a2) is the local magnified SEM image (30000 times) of the initial renewable biomass fiber; b1) is the SEM image (5000 times) of the thermosensitive polymer fiber obtained in Example 1; b2) is the SEM image (30000 times) of the thermosensitive polymer fiber obtained in Example 1.

[0043] Figure 2 The figures are the dispersion effect diagrams of the unmodified renewable biomass fiber and the thermosensitive polymer fiber prepared in Example 1 in water. Among them, the left figure in a) is the dispersion effect diagram of the unmodified renewable biomass fiber in water at room temperature, the right figure in a) is the dispersion effect diagram of the unmodified renewable biomass fiber in water at 50°C, the left figure in b) is the dispersion effect diagram of the thermosensitive polymer fiber prepared in Example 1 in water at room temperature, and the right figure in b) is the dispersion effect diagram of the thermosensitive polymer fiber prepared in Example 1 in water at 50°C.

[0044] Figure 3 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0045] Figure 4 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0046] Figure 5 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0047] Description of reference numerals:

[0048] 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0049] Hereinafter, the embodiments of the polyimide microspheres and their manufacturing methods, negative electrode plates, batteries and electrical devices of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0050] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0052] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0053] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0054] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0055] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0056] At present, the existing preparation process of temperature-sensitive fibers has the following shortcomings: first, the efficiency of electrospinning fiber production is low and difficult to mass produce; second, the strength of the output fiber is poor, and the fiber size is highly dependent on the equipment, and it is difficult to produce fibers of suitable size in one step, and it is often necessary to obtain the required length through subsequent process treatment; third, the spun polymer fiber has high solvent selectivity, poor solvent resistance, and small application space; fourth, subsequent modification often requires complex reactions such as atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT), which are difficult to operate and difficult to mass produce.

[0057] In order to solve the above technical problems, the present application develops a method for preparing temperature-sensitive polymer fibers that can be mass-produced by improving the preparation method; and the temperature-sensitive polymer fibers have the advantages of excellent temperature-sensitive properties, good mechanical properties, good thermal stability, and easily adjustable size, and therefore can be used in negative electrode slurry to improve the cycle performance of the battery.

[0058] [Thermosensitive polymer fiber]

[0059] In one embodiment of the present application, a first aspect of the present application provides a temperature-sensitive polymer fiber for negative electrode slurry, wherein the temperature-sensitive polymer fiber comprises a renewable biomass fiber and a temperature-sensitive polymer.

[0060] The properties of thermosensitive polymer fibers depend on the physical properties of biomass fibers, which have advantages such as good mechanical properties, good thermal stability, and easy-to-adjust dimensions. At the same time, the properties of thermosensitive polymer fibers also depend on the properties of thermosensitive polymers, whose own properties can change with temperature. Therefore, the switching of the hydrophilic and hydrophobic properties of the fiber surface can be achieved by controlling the external temperature: when the ambient temperature is lower than the low eutectic temperature, the fiber surface is hydrophilic, ensuring good suspension and dispersion of the fiber body in water; when the ambient temperature is higher than the low eutectic temperature, the fiber surface is hydrophobic, ensuring good suspension and dispersion of the fiber body in oily solvents.

[0061] Therefore, the application field of the temperature-sensitive polymer fiber provided in the present application is relatively wide. For example, it can be used in battery negative electrode slurry to improve the performance of the negative electrode plate: at the processing temperature (temperature lower than the low eutectic temperature), it can ensure its good dispersion in the slurry, and after coating, it constructs a three-dimensional network structure between the active coatings of the plate; during the baking process (temperature higher than the low eutectic temperature), the three-dimensional hydrophobic network formed by it can hinder the floating of the binder due to the capillary force formed in the plate during the evaporation of the solvent due to its own structural characteristics and the repulsion between the aqueous binder and the hydrophobic fiber network.

[0062] In some embodiments, the thermosensitive polymer is connected to the surface of the renewable biomass fiber. Optionally, the thermosensitive polymer is connected to the surface of the renewable biomass fiber through a coupling reaction or a polymerization reaction.

[0063] From the above, it can be seen that the use of temperature-sensitive polymer fibers in battery negative electrode slurry can prevent the floating of the binder due to capillary force formed in the electrode during solvent evaporation; however, adding unconnected fibers or temperature-sensitive polymers alone to the negative electrode slurry does not have such an advantage, but will instead deteriorate the performance of the battery cell.

[0064] In some embodiments, the coupling reaction or polymerization reaction includes at least one of an amide condensation reaction, a Schiff base reaction, an esterification reaction, and a free radical polymerization reaction.

[0065] Amide condensation and Schiff base reaction are both relatively mature methods for surface grafting modification. The range of condensation agents available is wide, and different condensation agents can be used to graft different reaction raw materials, such as: 2-(7-azabenzotriazole)-N,N,N',N'-tetramethyluronium hexafluorophosphate, dicyclohexylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, 1-hydroxybenzotriazole, etc.

[0066] In some embodiments, the solvent for the coupling reaction includes at least one of dichloromethane, 1,4-dioxane, toluene, xylene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, and water.

[0067] Selecting solvents with different polarities can ensure the dispersibility of biomass fibers modified with different coupling agents.

[0068] In some embodiments, the renewable biomass fibers include at least one of cellulose fibers, chitosan fibers, chitin fibers, silk fibers, and animal fibers.

[0069] The renewable biomass fibers selected in this application are characterized by wide sources and rich raw materials. Therefore, the thermosensitive polymer fibers of this application are easy to mass-produce. At the same time, the renewable biomass fibers selected in this application can endow the modified thermosensitive polymer fibers with the physical properties of the fibers themselves. For example, good mechanical properties, light weight, liquid retention, low linear thermal expansion coefficient, good thermal stability, and easily adjustable aspect ratio, etc., and thermosensitive polymer fibers with various excellent physical properties can be prepared.

[0070] However, other types of fibers do not have such characteristics. For example, the cost of rayon and bacterial cellulose is relatively high, and their strength and toughness are poor. When the thermosensitive polymer fibers synthesized from them are used in the negative electrode slurry, their improvement of battery performance is less.

[0071] In some embodiments, the surface of the renewable biomass fibers has chemical groups. Based on the mass of the renewable biomass fibers, the content of the chemical groups is 5-10 mmol / g, and can be optionally 10 mmol / g.

[0072] In some embodiments, the chemical groups include at least one of hydroxyl groups, amino groups, amide groups, and ester groups.

[0073] There are various active groups on the surface of the renewable biomass fibers selected in this application, and they have certain solvent resistance characteristics, and there is a large space for subsequent modification.

[0074] In some embodiments, the renewable biomass fibers have surface amino modification.

[0075] In some embodiments, the surface amino modification of the renewable biomass fibers is carried out by a silane coupling agent. The silane coupling agent includes at least one of aminopropyltrimethoxysilane and aminopropyltriethoxysilane. The mass ratio of the silane coupling agent to the renewable biomass fibers is 0.5-1:1, and can be optionally 1:1.

[0076] The selection of silane coupling agents with different end groups can provide sufficient possibilities for the surface modification of renewable biomass fibers and provide sufficient guarantees for the mass production of temperature-sensitive polymer fibers.

[0077] In some embodiments, the thermosensitive polymer includes at least one of poly(N-vinylcaprolactam), poly(N-isopropylacrylamide), poly(N,N-diethylacrylamide), poly(dicarboxyisopropylacrylamide), and poly[2-(N,N-dimethylamino)methacrylate].

[0078] In the present application, different thermosensitive polymers can be selected to prepare different thermosensitive polymer fibers. Since different thermosensitive polymers have different low melting temperatures, a wider temperature application window can be provided for the application of thermosensitive polymer fibers.

[0079] In some embodiments, the weight average molecular weight of the thermosensitive polymer is 5-20w, and can be 10w.

[0080] In this article, the term "weight average molecular weight" refers to the statistical average of the mass fractions of each fraction in the polymer. The polymer can be characterized by the sum of the weight fractions of molecules of different molecular weights multiplied by their corresponding molecular weights.

[0081] In the present application, the weight average molecular weight of the polymer can be tested by methods known in the art, such as gel chromatography, such as Waters 2695Isocratic HPLC gel chromatograph (differential refractive index detector 2141). In some embodiments, the test method is to use a polystyrene solution sample with a mass fraction of 3.0% as a reference, and select a matching chromatographic column (oily: Styragel HT5DMF7.8*300mm+Styragel HT4). Use purified N-methylpyrrolidone (NMP) solvent to prepare a 3.0% polymer glue, and let the prepared solution stand for one day for use. During the test, first use a syringe to draw tetrahydrofuran, rinse, and repeat several times. Then draw 5mL of the experimental solution, remove the air in the syringe, and wipe the needle tip dry. Finally, slowly inject the sample solution into the injection port. After the reading stabilizes, obtain the data and read the weight average molecular weight.

[0082] In some embodiments, the thermosensitive polymer has active group end-capping, and the active group end-capping includes at least one of carboxyl end-capping, acyl chloride end-capping, or aldehyde end-capping.

[0083] Similarly, different active groups can be selected to terminate the thermosensitive polymer to adapt to the mass production of thermosensitive polymer fibers.

[0084] In some embodiments, the diameter of the temperature-sensitive polymer fiber is 10 nm to 200 nm, and can be 50 nm to 100 nm.

[0085] In some embodiments, the length of the temperature-sensitive polymer fiber is 0.5 μm to 100 μm, and can be 10 to 50 μm.

[0086] In some embodiments, the aspect ratio of the temperature-sensitive polymer fiber is (20:1) to (2000:1), and can be optionally (200:1) to (800:1).

[0087] In some embodiments, the temperature change range of the temperature-sensitive polymer fiber is 37°C to 40°C, and can be 37°C.

[0088] The thermosensitive polymer fiber provided in this application has excellent properties and can be applied to a variety of fields. For example, adding thermosensitive fibers with the above characteristics in the preparation process of negative electrode sheets has many advantages. First, it has good thermosensitive properties: at the processing temperature (temperature lower than the low eutectic temperature), it can ensure good dispersion in the slurry, and construct a three-dimensional network structure between the active coatings of the electrode sheet after coating; during the baking process (temperature higher than the low eutectic temperature), the three-dimensional hydrophobic network formed by it can prevent the capillary force formed in the electrode sheet during the solvent evaporation process from causing the binder to float. Second, the thermosensitive fiber matrix has good toughness. The three-dimensional "interlocking" microstructure constructed by the fibers in the negative electrode sheet can enhance the cohesion of the electrode sheet, while hindering the release of stress in the electrode sheet, inhibiting the expansion of the electrode sheet, improving the cycle performance of the battery, and stabilizing the electrode, especially in the silicon negative electrode. Third, the network and channels built by the fiber itself are conducive to the wetting of the electrolyte and the transmission of lithium ions.

[0089] In some embodiments, based on the total mass of the negative electrode slurry, the content of the temperature-sensitive polymer fiber is 0.01 to 3 wt %, and may be 0.1 wt % to 0.5 wt %.

[0090] Adding a certain amount of temperature-sensitive polymer fibers into the negative electrode slurry can ensure the processing properties of the slurry, such as the filterability of the slurry.

[0091] In one embodiment of the present application, a method for preparing a temperature-sensitive polymer fiber for negative electrode slurry is also provided, wherein a temperature-sensitive polymer is connected to the surface of a renewable biomass fiber to obtain the temperature-sensitive polymer fiber.

[0092] In any embodiment, the method comprises the following steps:

[0093] Modifying the surface of the renewable biomass fiber with amino groups by using a silane coupling agent to obtain a renewable biomass fiber with amino groups modified on the surface;

[0094] The thermosensitive polymer is terminated with active groups to obtain an active group-terminated thermosensitive polymer;

[0095] The active group-terminated temperature-sensitive polymer is connected to the surface of the amino-modified renewable biomass fiber to obtain the temperature-sensitive polymer fiber for negative electrode slurry.

[0096] The present application proposes a method for preparing mass-producible thermosensitive polymer fibers, which uses renewable biomass fibers that can be mass-produced at tons level as a substrate, and grafts thermosensitive polymers on the surface through polymerization or coupling reactions. This not only solves the problem that traditional thermosensitive polymer fibers are difficult to mass-produce, but also prepares thermosensitive polymer fibers with excellent thermosensitive properties: when the ambient temperature is lower than the low eutectic temperature, it is hydrophilic; when the ambient temperature is higher than the low eutectic temperature, it is hydrophobic, and has a wide range of applications.

[0097] In some embodiments, the thermosensitive polymer is attached to the surface of the renewable biomass fiber through a coupling reaction or a polymerization reaction.

[0098] From the above, it can be seen that the use of temperature-sensitive polymer fibers in battery negative electrode slurry can prevent the floating of the binder due to capillary force formed in the electrode during solvent evaporation; however, adding unconnected fibers or temperature-sensitive polymers alone to the negative electrode slurry does not have such an advantage, but will instead deteriorate the performance of the battery cell.

[0099] In some embodiments, the coupling reaction or polymerization reaction includes at least one of an amide condensation reaction, a Schiff base reaction, an esterification reaction, and a free radical polymerization reaction.

[0100] Amide condensation reaction, Schiff base reaction, esterification reaction, and free radical polymerization reaction are all relatively mature methods for surface grafting modification. The range of condensation agents available is wide, and different condensation agents can be used to graft different reaction raw materials, for example: 2-(7-azabenzotriazole)-N,N,N',N'-tetramethyluronium hexafluorophosphate, dicyclohexylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, 1-hydroxybenzotriazole, etc.

[0101] [Negative electrode]

[0102] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0103] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0104] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. 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, 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, the present application is not limited to these materials, and other traditional 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.

[0106] In some embodiments, the negative electrode film layer may further 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).

[0107] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0108] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0109] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0110] In some embodiments, based on the total mass of the negative electrode slurry, the content of the temperature-sensitive polymer fiber is 0.01 to 3 wt %, and may be 0.1 to 0.5 wt %.

[0111] Adding a certain amount of temperature-sensitive polymer fibers into the negative electrode slurry can ensure the processing properties of the slurry, such as the filterability of the slurry.

[0112] [Positive electrode]

[0113] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0114] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0115] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0116] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries 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 may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 、LiMn2 O 4 )), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM 811 )、lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and at least one of its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of composite materials of lithium manganese iron phosphate and carbon.

[0117] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0118] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0120] [Electrolytes]

[0121] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.

[0122] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0123] In some embodiments, the electrolyte salt can 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0124] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0125] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0126] [Isolation film]

[0127] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0128] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0129] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be made into an electrode assembly through a winding process or a stacking process.

[0130] In some embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0131] In some embodiments, the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a pouch-type soft package. The material of the soft package may be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. may be cited.

[0132] [Lithium secondary battery]

[0133] The present application also provides a lithium secondary battery, and the lithium secondary battery includes a negative electrode paste, and the negative electrode paste includes the thermosensitive polymer fiber provided by the present application.

[0134] The present application has no particular limitation on the shape of the lithium secondary battery, and it may be cylindrical, square, or any other shape. For example, Figure 3 is a secondary battery 5 with a square structure as an example.

[0135] In some embodiments, referring to Figure 4 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of the electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select according to specific actual needs.

[0136] [Electric device]

[0137] In addition, the present application also provides an electric device, and the electric device includes the lithium secondary battery provided by the present application. The lithium secondary battery may be used as the power source of the electric device or as the energy storage unit of the electric device. The electric device may include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0138] As the electrical device, a lithium secondary battery can be selected according to its usage requirements.

[0139] Figure 5 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of lithium secondary batteries, a battery pack or a battery module can be used.

[0140] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a lithium secondary battery may be used as a power source.

[0141] Example

[0142] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0143] 1. Preparation method

[0144] Example 1

[0145] 1.1 Preparation of thermosensitive polymer fibers

[0146] (1) Preparation of surface amino-modified fibers

[0147] 10.0 g of cellulose fiber was dispersed in ethanol / water mixed solvent (200 mL, V / V=4 / 1), 10.0 g of aminopropyltrimethoxysilane was added, and the mixed system was reacted at 70° C. for 12 h. After the reaction, the mixed solution was centrifuged 3 times and vacuum dried to obtain fiber powder with surface amino modification.

[0148] (2) Preparation of active group-terminated poly (N-vinyl caprolactam)

[0149] 10.0g of N-vinyl caprolactam was dissolved in 200mL of 1,4-dioxane, 0.3g of azobisisobutyronitrile was added to the system, nitrogen was passed for 30min, and then thioglycolic acid was added, and the reaction was carried out at 70°C for 12h. After the reaction was completed, 1,4-dioxane was removed by vacuum distillation, and the obtained solid was redissolved in dichloromethane. The dichloromethane solution of carboxyl-terminated poly(N-vinyl caprolactam) was slowly added dropwise to petroleum ether for precipitation and purification, and the mixed solution was filtered to obtain a solid; the above operation was repeated 3 times and then placed in a vacuum drying oven for drying to obtain carboxyl-terminated poly(N-vinyl caprolactam).

[0150] 10.0 g of carboxyl-terminated poly(N-vinyl caprolactam) was dissolved in 200 mL of toluene, 1 mL of N,N-dimethylformamide was added, the system was heated to 70 °C, and 10 mL of thionyl chloride (SOCl) was slowly added dropwise. 2 ), react at 70°C for 12h. The final reaction solution was slowly added dropwise to petroleum ether for precipitation and purification, and the mixed solution was filtered to obtain a solid; the above operation was repeated 3 times and then placed in a vacuum drying oven for drying to obtain poly(N-vinyl caprolactam) terminated with acyl chloride.

[0151] (3) Preparation of temperature-sensitive polymer fibers

[0152] 10.0 g of acyl chloride-terminated poly (N-vinyl caprolactam) was dissolved in 200 mL of N-vinyl pyrrolidone, and the system temperature was cooled to 0°C, and the surface amino-modified fiber was added, and the reaction was carried out at 0°C for 12 hours. After the reaction, the mixture was centrifuged and washed with ethanol three times to obtain the surface poly (N-vinyl caprolactam)-modified nanofiber, which was recorded as A1.

[0153] 1.2 Preparation of negative electrode

[0154] A dispersant for negative electrode (1.0%), cellulose thermosensitive fiber (the added amount accounts for 0.3% of the mass of the active coating, 30μm, aspect ratio 600:1), and a plasticizer (0.5%) are uniformly dispersed in an aqueous solution. A conductive agent for negative electrode (1.0%) and an active material (95.0%) are added to the aqueous solution after being mixed in advance. After stirring for a period of time, a binder for negative electrode (2.0%) is added. After being fully stirred and sieved, the slurry is applied to the negative electrode collector according to the corresponding coating weight. The above-mentioned pole pieces are rolled and cut to obtain negative pole pieces for use.

[0155] 1.3 Preparation of positive electrode

[0156] The positive electrode binder and N-methylpyrrolidone are fully mixed to form a uniform transparent glue solution, the positive electrode conductive agent is added to the glue solution and fully stirred, and the positive electrode active material is added after mixing, and the slurry is sieved after fully stirring, and then coated on the positive electrode current collector, and the positive electrode sheet is obtained after rolling and cutting for use.

[0157] 1.4 Preparation of batteries

[0158] The coated diaphragm and the positive electrode sheet and the negative electrode sheet are assembled into a bare battery cell by lamination or winding, and then the secondary battery is obtained by top and side sealing, high temperature baking, liquid injection, formation, liquid injection, and capacity measurement.

[0159] Embodiment 2-3

[0160] The preparation methods of the temperature-sensitive polymer fibers in Examples 2 to 3 are basically similar to those in Example 1, but the types of biomass fibers are changed. The specific parameters are shown in Table 1-2.

[0161] Example 4

[0162] The preparation method of the temperature-sensitive polymer fiber in Example 4 is basically similar to that in Example 1, but the content of the chemical groups on the biomass fiber is changed. The specific parameters are shown in Table 1-2.

[0163] Embodiment 5-6

[0164] The preparation methods of the temperature-sensitive polymer fibers in Examples 5 to 6 are basically similar to those in Example 1, but the types of coupling reagents are changed. The specific parameters are shown in Table 1-2.

[0165] Example 7

[0166] The preparation method of the temperature-sensitive polymer fiber in Example 7 is basically similar to that in Example 1, but the mass ratio of the coupling agent to the renewable biomass fiber is changed. The specific parameters are shown in Table 1-2.

[0167] Embodiments 8 to 11

[0168] The preparation methods of the temperature-sensitive polymer fibers in Examples 8 to 11 are basically similar to those in Example 1, but the types of the temperature-sensitive polymers are changed. The specific parameters are shown in Table 1-2.

[0169] Embodiments 12 to 13

[0170] The preparation methods of the temperature-sensitive polymer fibers in Examples 12 to 13 are basically similar to those in Example 1, but the weight average molecular weight of the temperature-sensitive polymer is changed. The specific parameters are shown in Table 1-2.

[0171] Embodiments 14 to 15

[0172] The preparation methods of the temperature-sensitive polymer fibers in Examples 14 to 15 are basically similar to those in Example 1, but the types of active group end-capping are changed. The specific parameters are shown in Table 1-2.

[0173] Embodiments 16 to 17

[0174] The preparation method of the temperature-sensitive polymer fiber in Examples 16 to 17 is basically similar to that in Example 1, but the aspect ratio of the temperature-sensitive polymer fiber is changed. The specific parameters are shown in Table 1-2.

[0175] Embodiment 18

[0176] The preparation method of the temperature-sensitive polymer fiber in Example 18 is basically similar to that in Example 1, but the temperature change range of the temperature-sensitive polymer fiber is changed. The specific parameters are shown in Table 1-2.

[0177] Embodiments 19 to 20

[0178] The preparation methods of the batteries in Examples 19 to 20 are basically similar to those in Example 1, but the content of the temperature-sensitive polymer fiber (based on the total mass of the negative electrode slurry) is changed. The specific parameters are shown in Table 1-2.

[0179] Comparative Examples 1-2

[0180] The preparation methods of the temperature-sensitive polymer fibers in Comparative Examples 1-2 are basically similar to that in Comparative Example 1, but the types of biomass fibers are changed. The specific parameters are shown in Table 1-2.

[0181] Comparative Example 3

[0182] The preparation method of the temperature-sensitive polymer fiber in Comparative Example 3 is basically similar to that in Comparative Example 1, but the type of the temperature-sensitive polymer is changed. The specific parameters are shown in Table 1-2.

[0183] Comparative Example 4

[0184] The preparation method of the temperature-sensitive polymer fiber in Comparative Example 4 is basically similar to that in Comparative Example 1, but the weight average molecular weight of the temperature-sensitive polymer is changed. The specific parameters are shown in Table 1-2.

[0185] Comparative Example 5

[0186] The preparation method of the temperature-sensitive polymer fiber in Comparative Example 5 is basically similar to that in Comparative Example 1, but the aspect ratio of the temperature-sensitive polymer fiber is changed. The specific parameters are shown in Table 1-2.

[0187] Comparative Example 6

[0188] The preparation method of the battery in Comparative Example 6 is basically similar to that in Comparative Example 1, but the content of the temperature-sensitive polymer fiber (based on the total mass of the negative electrode slurry) is changed. The specific parameters are shown in Table 1-2.

[0189] Comparative Examples 7 to 8

[0190] The preparation methods of the batteries in Comparative Examples 7 to 8 are basically similar to those in Comparative Example 1, but no temperature-sensitive polymer fibers are added to the negative electrode slurry, and: the temperature-sensitive polymer is added alone to the negative electrode slurry in Comparative Example 7; the fiber is added alone to the negative electrode slurry in Comparative Example 8, and the specific parameters are shown in Table 1-2.

[0191] Table 1 Preparation parameters

[0192]

[0193] Table 2 Preparation parameters

[0194]

[0195] 2. Performance Test Method

[0196] 1. Performance test method of temperature-sensitive polymer fibers

[0197] (1) Suspension time test

[0198] Take 0.2 g of fiber and disperse it in a 100 mL measuring cylinder. After shaking and dispersion, let it stand for 1 hour and observe the height of the fiber layer (corresponding unit mL).

[0199] (2) Mechanical properties test

[0200] 100 mL of fiber dispersion with a solid content of 2% was placed in a glass dish to allow the water in the dispersion to evaporate naturally to form a film. The obtained fiber film was cut into 1x5 cm rectangular strips and stretched at 2 mm / min using an INSTRON 3365 universal tensile testing machine to test its tensile strength and elongation at break (the average value of 3 to 5 strips tested).

[0201] (3) Acid and alkali resistance test

[0202] A NaOH solution with a pH value of 11 and a HCl solution with a pH value of 3 were prepared, and the fiber matrix was subjected to an acid and alkali resistance test at a high temperature of 70°C (immersed for 60 days). The fiber length change was measured by SEM to test the acid and alkali resistance of the fiber.

[0203] (4) Hydrophilicity and hydrophobicity response time test

[0204] The thermosensitive fiber is dispersed in water at a certain solubility, and its aqueous dispersion is instantly placed in water corresponding to the critical temperature of the thermosensitive polymer, and the time from the beginning of sedimentation to complete sedimentation is recorded.

[0205] 2. Battery cycle performance test method

[0206] Test the battery's room temperature cycle performance according to the following process:

[0207] 1)Rest 30min 25 10

[0208] 2) 1 / 3C DC 2.8V 25 10

[0209] 3)Rest 30min 25 10

[0210] 4)1 / 3C CC 4.25V CV 0.05C 25 10

[0211] 5)Rest 30min 25 10

[0212] 6) 1 / 3C DC 2.8V 25 10Cn (this step is recorded as the actual capacity Cn)

[0213] 7)Rest 30min 25 10

[0214] Serial number cycle (three elements, taking 25℃ as an example) Temperature (℃) Sampling interval (S)

[0215] Remark

[0216] 1) Adjust the temperature to 25℃

[0217] 2)Rest 2h 25 30

[0218] 3)0.5C CC 4.25V CV 0.05C 25 30

[0219] 4)Rest 10min 25 30

[0220] 5) 1C DC 2.8 25 30F (this step is to calculate Fading)

[0221] 6) rest 10min 25 30

[0222] 7) Repeat steps 3-6 until the capacity Fading ≤ 80% 25 30

[0223] III. Analysis of test results of various embodiments and comparative examples

[0224] Secondary batteries of various embodiments and comparative examples were prepared according to the above method, and various parameters were measured. The results are shown in Table 3 below.

[0225] Table 3 Performance parameters

[0226]

[0227]

[0228] 1. Characterization of properties of thermosensitive polymer fibers

[0229] (1) Morphology measurement

[0230] The surface morphology of the initial unmodified renewable biomass fiber and the thermosensitive polymer fiber prepared in Example 1 was measured using a Zeiss Sigma-300 scanning electron microscope. The test results are as follows: Figure 1 As shown. Figure 1 It can be seen that the initial renewable biomass fibers are well dispersed in aqueous solution because their surfaces are rich in hydrophilic groups such as hydroxyl and amino groups and the temperature of the thermosensitive polymer fibers is below the low eutectic temperature; in addition, the surface of the fibers grafted with the thermosensitive polymer becomes significantly rougher than that of the initial renewable biomass fibers, proving that the thermosensitive polymer has been successfully grafted.

[0231] (2) Determination of phase transition temperature

[0232] The phase transition temperature measurement results of the initial unmodified renewable biomass fiber and the thermosensitive polymer fiber prepared in Example 1 are as follows: Figure 2 shown. Figure 2 It shows that the initial renewable biomass fibers can be well dispersed in aqueous solution at room temperature and 50°C (higher than the low eutectic temperature of 37°C), and its surface properties have not changed significantly at the two temperatures; the polymer-grafted renewable biomass fibers can be well dispersed in aqueous solution at room temperature, but at 50°C (higher than the low eutectic temperature of 37°C), the polymer-grafted biomass fibers will quickly settle to the bottom of the sample bottle. This is because the temperature-sensitive polymer on the surface of the biomass fibers collapses, and the surface is converted from the initial hydrophilic to hydrophobic.

[0233] 2. Performance testing of temperature-sensitive polymer fibers and batteries

[0234] The performance test results of the temperature-sensitive polymer fiber and battery are shown in Table 3.

[0235] In Examples 1 to 20, the prepared temperature-sensitive polymer fibers have good properties, including suspension, mechanics, acid and alkali resistance, hydrophilic and hydrophobic response, etc.; at the same time, the batteries containing the temperature-sensitive polymer fibers in the negative electrode slurry have excellent cycle performance.

[0236] In the negative electrode slurry of Comparative Example 7, no temperature-sensitive polymer fiber is added, but a temperature-sensitive polymer is added; in the negative electrode slurry of Comparative Example 8, no temperature-sensitive polymer fiber is added, but renewable biomass fiber is added. From the comparison between Examples 1 to 20 and Comparative Examples 7 to 8, it can be seen that adding temperature-sensitive polymer fiber to the negative electrode slurry can effectively improve the cycle performance of the battery; while adding unprocessed temperature-sensitive polymer or fiber to the negative electrode slurry cannot improve the battery performance.

[0237] It can be seen from Examples 1 to 4 that when preparing temperature-sensitive polymer fibers, using a variety of different types of renewable biomass fibers (such as cellulose fibers, chitosan fibers, chitin fibers), or using renewable biomass fibers with different contents of surface chemical groups (such as 5 mmol / g, 10 mmol / g), can make the prepared temperature-sensitive polymer fibers have better performance, and the battery containing the temperature-sensitive polymer fibers in the negative electrode slurry can have better cycle performance.

[0238] In Comparative Examples 1 to 2, when preparing the thermosensitive polymer fibers, artificial fibers, bacterial cellulose, etc. are used to replace the renewable biomass fibers in Examples 1 to 4. The comprehensive performance of the prepared thermosensitive polymer fibers is poor, and the addition of the negative electrode slurry cannot effectively improve the cycle performance of the battery.

[0239] It can be seen from Examples 1 and 5 to 7 that when preparing the temperature-sensitive polymer fibers, using a variety of different types of silane coupling agents (for example, aminopropyltrimethoxysilane, aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane), or using silane coupling agents in different mass ratios (for example, the mass ratio of silane coupling agent to renewable biomass fiber is 1:1, 0.5:1), the prepared temperature-sensitive polymer fibers can have better performance, and the battery containing the temperature-sensitive polymer fibers in the negative electrode slurry can have better cycle performance.

[0240] It can be seen from Examples 1 and 8 to 15 that when preparing thermosensitive polymer fibers, using a variety of different types of thermosensitive polymers (for example, poly(N-vinylcaprolactam), poly(N-isopropylacrylamide), poly-N,N-diethylacrylamide, poly(dicarboxyisopropylacrylamide), poly[methacrylate-2-(N,N-dimethylamino)] ester), or using thermosensitive polymers with different molecular weights (for example, 5W, 10W, 20W), or using different active group end-capping (for example, acyl chloride end-capping, carboxyl end-capping, aldehyde end-capping), the prepared thermosensitive polymer fibers can have better performance, and the battery containing the thermosensitive polymer fibers in the negative electrode slurry can have better cycle performance.

[0241] In Comparative Example 3, polyacrylic acid was used as the thermosensitive polymer when preparing the thermosensitive polymer fiber; in Comparative Example 4, a thermosensitive polymer with a molecular weight of 1W was used when preparing the thermosensitive polymer fiber. The comprehensive performance of the thermosensitive polymer fibers prepared in Comparative Examples 3 to 4 was poor, and the addition of the negative electrode slurry could not effectively improve the cycle performance of the battery.

[0242] It can be seen from Examples 1 and 16 to 18 that the use of temperature-sensitive polymer fibers with different aspect ratios (e.g., 600:1, 20:1, 2000:1) or temperature-sensitive polymer fibers with different temperature ranges (e.g., 37°C, 40°C) can make the battery containing the temperature-sensitive polymer fibers in the negative electrode slurry have better cycle performance.

[0243] In Comparative Example 5, a thermosensitive polymer fiber with an aspect ratio of 10:1 was used, and its addition to the negative electrode slurry could not effectively improve the cycle performance of the battery. From the comparison between Examples 1 to 20 and Comparative Example 5, it can be seen that controlling the aspect ratio of the thermosensitive polymer fiber in the negative electrode slurry within a suitable range can improve the cycle performance of the lithium secondary battery.

[0244] It can be seen from Examples 1 and 19 to 20 that adding different amounts of temperature-sensitive polymer fibers (e.g., 0.01wt%, 0.3wt%, 3wt%) into the negative electrode slurry can make the battery containing the temperature-sensitive polymer fibers in the negative electrode slurry have better cycle performance.

[0245] In the negative electrode slurry of Comparative Example 6, 0.005 wt% of the temperature-sensitive polymer fiber is added, which cannot effectively improve the cycle performance of the battery. From the comparison between Examples 1 to 20 and Comparative Example 6, it can be seen that controlling the content of the temperature-sensitive polymer fiber in the negative electrode slurry within a suitable range can improve the cycle performance of the lithium secondary battery.

[0246] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A temperature-sensitive polymer fiber for negative electrode slurry, It is characterized in that The temperature-sensitive polymer fiber includes renewable biomass fiber and a temperature-sensitive polymer.

2. The temperature-sensitive polymer fiber according to claim 1, It is characterized in that The renewable biomass fiber includes at least one of cellulose fiber, chitosan fiber, chitin fiber, silk fiber and animal fiber.

3. The temperature-sensitive polymer fiber according to claim 2, It is characterized in that The surface of the renewable biomass fiber has chemical groups, and based on the mass of the renewable biomass fiber, the content of the chemical groups is 5 to 10 mmol / g, and can be 10 mmol / g.

4. The temperature-sensitive polymer fiber according to claim 3, It is characterized in that The chemical group includes at least one of a hydroxyl group, an amine group, an amide group, and an ester group.

5. The temperature-sensitive polymer fiber according to claim 1, It is characterized in that The temperature-sensitive polymer includes at least one of poly(N-vinylcaprolactam), poly(N-isopropylacrylamide), poly(N,N-diethylacrylamide), poly(dicarboxyisopropylacrylamide), and poly[2-(N,N-dimethylamino)methacrylate].

6. The temperature-sensitive polymer fiber according to claim 5, It is characterized in that The weight average molecular weight of the temperature-sensitive polymer is 5-20w, and can be 10w.

7. The temperature-sensitive polymer fiber according to claim 1, It is characterized in that The thermosensitive polymer is connected to the surface of the renewable biomass fiber. Optionally, the thermosensitive polymer is connected to the surface of the renewable biomass fiber through a coupling reaction or a polymerization reaction.

8. The temperature-sensitive polymer fiber according to claim 7, It is characterized in that The coupling reaction or polymerization reaction includes at least one of an amide condensation reaction, a Schiff base reaction, an esterification reaction, and a free radical polymerization reaction.

9. The temperature-sensitive polymer fiber according to claim 7, It is characterized in that The renewable biomass fiber has surface amino modification.

10. The temperature-sensitive polymer fiber according to claim 9, It is characterized in that The surface of the renewable biomass fiber is amino-modified by a silane coupling agent, wherein the silane coupling agent includes at least one of aminopropyltrimethoxysilane and aminopropyltriethoxysilane, and the mass ratio of the silane coupling agent to the renewable biomass fiber is (0.5-1):1, and can be optionally 1:

1.

11. The temperature-sensitive polymer fiber according to claim 7, It is characterized in that The thermosensitive polymer has active group end-capping, and the active group end-capping includes at least one of carboxyl end-capping, acyl chloride end-capping, or aldehyde end-capping.

12. The temperature-sensitive polymer fiber according to claim 1, It is characterized in that The diameter of the temperature-sensitive polymer fiber is 10 nm to 200 nm, and can be optionally 50 nm to 100 nm.

13. The temperature-sensitive polymer fiber according to claim 1, It is characterized in that The length of the temperature-sensitive polymer fiber is 0.5 μm to 100 μm, and can be optionally 10 to 50 μm.

14. The temperature-sensitive polymer fiber according to claim 12 or 13, It is characterized in that The aspect ratio of the temperature-sensitive polymer fiber is (20:1) to (2000:1), and can be optionally (200:1) to (800:1).

15. The temperature-sensitive polymer fiber according to claim 1, It is characterized in that The temperature variation range of the temperature-sensitive polymer fiber is 37° C. to 40° C., and can be selected as 37° C.

16. The temperature-sensitive polymer fiber according to claim 1, It is characterized in that Based on the total mass of the negative electrode slurry, the content of the temperature-sensitive polymer fiber is 0.01 to 3 wt %, and can be optionally 0.1 wt % to 0.5 wt %.

17. A method for preparing the temperature-sensitive polymer fiber according to any one of claims 1 to 16, It is characterized in that The thermosensitive polymer is connected to the surface of renewable biomass fiber to obtain the thermosensitive polymer fiber.

18. The preparation method according to claim 17, It is characterized in that The method comprises the following steps: Modifying the surface of the renewable biomass fiber with amino groups by using a silane coupling agent to obtain a renewable biomass fiber with amino groups modified on the surface; The thermosensitive polymer is terminated with active groups to obtain an active group-terminated thermosensitive polymer; The active group-terminated temperature-sensitive polymer is connected to the surface of the amino-modified renewable biomass fiber to obtain the temperature-sensitive polymer fiber for negative electrode slurry.

19. The preparation method according to claim 18, It is characterized in that The thermosensitive polymer is connected to the surface of the renewable biomass fiber through a coupling reaction or a polymerization reaction.

20. The preparation method according to claim 19, It is characterized in that The coupling reaction or polymerization reaction includes at least one of an amide condensation reaction, a Schiff base reaction, an esterification reaction, and a free radical polymerization reaction.

21. A lithium secondary battery, It is characterized in that The lithium secondary battery includes a negative electrode slurry including the temperature-sensitive polymer fiber according to any one of claims 1 to 16.

22. An electrical device, It is characterized in that Includes the lithium secondary battery described in claim 21.

Images