Positive electrode fluoride-free binder as well as preparation method and application thereof

Abstract

The invention discloses a positive electrode fluoride-free binder and a preparation method and application thereof, and belongs to the technical field of binder preparation. The positive electrode fluoride-free binder provided by the invention is prepared from the following components in percentage by mass: 40-90% of polyvinyl alcohol and glycerol; 10 to 60% of keratin; the mass ratio of the polyvinyl alcohol to the glycerol is 22: 3. According to the positive electrode fluoride-free binder provided by the invention, abundant polar groups contained in keratin, hydroxyl groups of polyvinyl alcohol and hydroxyl groups of glycerol interact through non-covalent hydrogen bonds, so that a binder network structure with enhanced cohesion is constructed, and the mechanical property and the structural stability of a positive electrode can be improved; after the assembled button half-cell is activated for 3 circles at 0.1 C and then circulated for 400 circles at 2C, the specific capacity is 482mAh / g, and the button half-cell has excellent cycling stability.

Description

Technical Field

[0001] The present application belongs to the technical field of binder preparation, and in particular relates to a positive electrode fluorine-free binder and a preparation method and application thereof. Background Art

[0002] Lithium-sulfur batteries (LSBs) are considered one of the most promising alternatives due to their exceptional theoretical specific capacity (1675 mAh / g) and energy density (2600 Wh / kg). They are sufficient to meet the high-performance lithium battery needs of 5G high-power electronic products and have potential commercial applications. In lithium-sulfur battery systems, electrode materials are the core factor determining battery performance, and binders, as an indispensable component of electrode materials, have a direct impact on the battery's electrochemical performance.

[0003] Currently, polyvinylidene fluoride (PVDF) is the predominant commercial cathode binder, which performs well in terms of electrochemical stability, adhesion, and ion mobility. However, as market demands for battery energy density continue to increase, PVDF has exposed numerous limitations when adapting to lithium-sulfur batteries with high energy / power density and long cycle life, making it difficult to meet industry development needs. The development of a binder with better overall performance is urgent.

[0004] When sulfur is used as a cathode material in lithium batteries, it still faces key challenges: on the one hand, the shuttle effect between soluble lithium polysulfide (LiPS) intermediates and commonly used liquid electrolytes in LSBs systems, which leads to poor cycling stability; on the other hand, the significant volume change (≈80%) of sulfur materials during lithiation / delithiation, which stems from the density difference between Li2S and S8, thus limiting the excellent performance of lithium-sulfur batteries. Therefore, in order to improve electrode capacity and cycling stability and reduce the volume change of active materials during charge and discharge, it is crucial to maintain the integrity of sulfur cathode materials, which also places higher requirements on the performance of the binder. Summary of the Invention

[0005] The present application discloses a positive electrode fluorine-free binder and its preparation method and application, aiming to solve the technical problems of poor adhesion and mechanical properties of existing positive electrode fluorine-free binders, which lead to poor electrochemical performance and poor cycle capacity of lithium-sulfur batteries.

[0006] In order to achieve the above objectives, the technical solution of this application is:

[0007] The first aspect of the present application provides a positive electrode fluorine-free binder, which is composed of the following components by mass percentage:

[0008] Polyvinyl alcohol and glycerol 40-90%;

[0009] Keratin 10-60%;

[0010] The mass ratio of the polyvinyl alcohol to glycerol is 22:3.

[0011] In combination with the first aspect, preferably, the mass percentage of keratin is 20-50%.

[0012] In combination with the first aspect, preferably, the mass percentage of keratin is 30%.

[0013] In combination with the first aspect, preferably, the molecular weight of the polyvinyl alcohol is 20-25 kDa, and the degree of alcoholysis is 98-99% (mol / mol).

[0014] The second aspect of the present application provides a method for preparing the positive electrode fluorine-free binder according to the first aspect, the preparation method comprising:

[0015] The positive electrode fluorine-free binder is obtained by reacting keratin, polyvinyl alcohol and glycerol in water and then freeze-drying the reactants.

[0016] In combination with the second aspect, preferably, the time for reacting keratin, polyvinyl alcohol and glycerin in water is 2-4 hours.

[0017] In combination with the second aspect, preferably, the freeze-drying time is 36-48 hours.

[0018] The third aspect of the present application provides use of the positive electrode fluorine-free binder described in the first aspect or the positive electrode fluorine-free binder prepared by the preparation method described in the second aspect in preparing a sulfur positive electrode.

[0019] The fourth aspect of the present application provides a sulfur positive electrode material, comprising a positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode fluorine-free binder, and the positive electrode fluorine-free binder is the positive electrode fluorine-free binder described in the first aspect.

[0020] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application include at least:

[0021] The fluorine-free positive electrode binder provided by this application is prepared by combining polyvinyl alcohol, glycerol and keratin. On the one hand, the abundant polar groups contained in keratin, the hydroxyl groups of polyvinyl alcohol and the hydroxyl groups of glycerol interact through non-covalent hydrogen bonds to construct a binder network structure with enhanced cohesion, which can improve the mechanical properties and structural stability of the positive electrode. On the other hand, the raw materials are bound together by hydrogen bonds, which has significant storage resistance and can ensure the stable cycle performance of lithium-sulfur batteries. At the same time, the button half-cell prepared using the binder prepared by this application was activated at 0.1C for 3 cycles and then cycled at 2C for 400 cycles, showing a specific capacity of 482mAh / g, with excellent cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some of the embodiments described in this application. Those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0023] Figure 1 Infrared spectra of polyvinyl alcohol (PVA), glycerol (GL), keratin (α-HP) and A1-positive electrode fluorine-free binder provided in the examples of this application;

[0024] Figure 2 The peeling test diagrams of A1-positive electrode fluorine-free binder, A2-positive electrode fluorine-free binder, PVDF, and PVA / GL provided in the examples of this application;

[0025] Figure 3 Electrochemical impedance spectroscopy of lithium-sulfur batteries with sulfur positive electrodes made of the A1-positive electrode fluorine-free binder, A2-positive electrode fluorine-free binder, PVDF, and PVA / GL provided in the examples of the present application before charge and discharge cycles;

[0026] Figure 4 Electrochemical impedance spectroscopy (EIS) of lithium-sulfur batteries with sulfur positive electrodes made from the A1-positive electrode fluorine-free binder, A2-positive electrode fluorine-free binder, PVDF, and PVA / GL provided in the examples of this application after 100 cycles at 1C;

[0027] Figure 5 The cycling performance diagram of lithium-sulfur batteries with sulfur positive electrodes made of A1-positive electrode fluorine-free binder, A2-positive electrode fluorine-free binder, PVDF, and PVA / GL provided in the examples of this application at 2C;

[0028] Figure 6 Cycling performance diagram of lithium-sulfur batteries with sulfur positive electrodes made of A1-positive electrode fluorine-free binder, A2-positive electrode fluorine-free binder, PVDF, and PVA / GL provided in the examples of this application at 0.1C;

[0029] Figure 7 This is a rate performance diagram of a lithium-sulfur battery with a sulfur positive electrode made of the A1-positive electrode fluorine-free binder provided in an embodiment of the present application at different current densities. DETAILED DESCRIPTION

[0030] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0031] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, B exists alone, and both A and B exist. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0032] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0033] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0034] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0035] It should be noted that all raw materials and reagents in the examples of the present application were purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0036] In a first aspect, the present invention provides a positive electrode fluorine-free binder, which is composed of the following components by mass percentage:

[0037] Polyvinyl alcohol and glycerol 40-90%;

[0038] Keratin 10-60%;

[0039] The mass ratio of the polyvinyl alcohol to glycerol is 22:3.

[0040] In one aspect, the cohesive force of the binder network structure is enhanced by the non-covalent hydrogen bond interaction between the polar groups contained in the keratin, the hydroxyl groups of the polyvinyl alcohol and the hydroxyl groups of the glycerol, which can improve the mechanical properties and structural stability of the positive electrode; on the other hand, the raw materials are combined by hydrogen bond, which has significant storage resistance and can ensure the stable cycle performance of the lithium-sulfur battery; at the same time, the specific capacity of the button half-cell prepared by the binder of the application is 482mAh / g after 3 cycles of activation at 0.1C and 400 cycles at 2C, which has excellent cycle stability.

[0041] In the embodiments of the present application, the polyvinyl alcohol and glycerol are preferably 40-90%, the keratin is preferably 10-60%, more preferably 20-50%, and more preferably 30%. The cohesive force is enhanced by the strong hydrogen bond interaction between the carbonyl groups in the keratin and the hydroxyl groups of the polyvinyl alcohol and glycerol. Too much keratin α-HP (α-HP content of 50%) cannot achieve better adhesion strength and mechanical strength.

[0042] In the embodiments of the present application, the molecular weight (M n ) of the polyvinyl alcohol is 20-25kDa, and the alcoholysis degree is 98-99% (mol / mol). The high alcoholysis degree of the polyvinyl alcohol has strong hydrophilicity and strong molecular chain polarity, and is easy to form hydrogen bonds, which is more suitable for water-based binders and can further improve the strength. The high molecular weight polyvinyl alcohol has a long molecular chain and a large contact area, and has a stronger intermolecular force and higher bonding strength.

[0043] It should be noted that the source of keratin used in the present application is not particularly limited and can be purchased on the market or prepared according to conventional methods known to those skilled in the art. For example, the following method can be used for preparation: soaking wool fibers in acetone for 8 hours, washing with ethanol three times; immersing the washed wool fibers in a deionized water solution containing urea, sodium dodecyl sulfate and sodium sulfide, heating and stirring; filtering the stirred solution, taking the yellow crude keratin solution obtained by filtration, dialyzing in deionized water for 5 days; rotary evaporation of the dialyzed solution, followed by freeze-drying to obtain white keratin. The structure of the prepared keratin is shown in formula 1:

[0044]

[0045] The second aspect of the present application provides a preparation method of the positive electrode fluorine-free binder of the first aspect, which comprises:

[0046] After the keratin, polyvinyl alcohol and glycerol are reacted in water, freeze-drying is performed to obtain the positive electrode fluorine-free binder.

[0047] In the embodiment of the present application, the time for reacting keratin, polyvinyl alcohol and glycerin in water is preferably 2-4 hours.

[0048] In the examples of the present application, the freeze-drying time is preferably 36-48 hours. The freeze-drying time required for aqueous solutions with different water contents varies. Generally speaking, for every 10% increase in initial water content, the drying time may be extended by 10%-15%. The water content in the examples of the present application is generally 70-75%, so the freeze-drying time includes a pre-freezing time of 6 hours to 12 hours and a sublimation time of 30 hours to 36 hours.

[0049] The third aspect of this application provides the use of the positive electrode fluorine-free binder described in the first aspect or the positive electrode fluorine-free binder prepared by the preparation method described in the second aspect in the preparation of a sulfur positive electrode. Among them, the positive electrode fluorine-free binder prepared based on the above has excellent bonding force, which can give the sulfur positive electrode excellent mechanical properties and structural stability; it also effectively buffers the mechanical stress caused by the volume expansion of sulfur during the charge and discharge process through the three-dimensional cross-linked structure, inhibiting electrode cracking and active material shedding. In addition, the introduction of fluorine-free elements significantly reduces the risk of electrolyte swelling and side reactions, providing a green and environmentally friendly bonding solution for the large-scale preparation of high-safety lithium-sulfur batteries.

[0050] A fourth aspect of the present application provides a sulfur cathode material comprising a cathode active material layer, wherein the cathode active material layer comprises a fluorine-free cathode binder, wherein the fluorine-free cathode binder is the fluorine-free cathode binder described in the first aspect. The sulfur cathode material, which exhibits high sulfur loading, good electronic conductivity, and structural stability, imparts excellent cycling stability to a lithium-sulfur battery.

[0051] It should be noted that the sulfur cathode material prepared in this application demonstrates significant application potential and unique advantages in lithium-sulfur batteries. It can adapt to the high specific energy requirements of lithium-sulfur batteries and performs outstandingly in key indicators such as cycle stability and rate performance. However, these excellent properties have not been demonstrated in other types of battery systems such as lithium-ion batteries and sodium-ion batteries. Therefore, the high compatibility of this sulfur cathode material with lithium-sulfur battery systems has also expanded a valuable technical path for the practical application of lithium-sulfur batteries.

[0052] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0053] Example 1

[0054] This embodiment provides a method for preparing an A1-positive electrode fluorine-free binder (0.3α-HP / PVA / GL), which specifically includes:

[0055] 0.616 g polyvinyl alcohol (PVA, M n≈20.5kDa), 0.084g glycerol (GL) was dissolved in 2.5g deionized water and stirred at 90°C for 5 hours (the resistivity of deionized water was 18.25MΩ.m); 0.3g keratin (α-HP) was dissolved in 2.5g deionized water and stirred at room temperature for 2 hours; the two solutions were mixed and stirred at room temperature for 2 hours to obtain a mixed colloidal solution, which was freeze-dried for 48 hours to obtain an A1-positive electrode fluorine-free binder (0.3α-HP / PVA / GL).

[0056] Example 2

[0057] This embodiment provides a method for preparing an A2-positive electrode fluorine-free binder (0.5α-HP / PVA / GL), which specifically includes:

[0058] 0.44 g polyvinyl alcohol (PVA, M n ≈20.5kDa), 0.06g glycerol (GL) was dissolved in 2.5g deionized water and stirred at 90°C for 5 hours (the resistivity of deionized water was 18.25MΩ.m); 0.5g keratin (α-HP) was dissolved in 2.5g deionized water and stirred at room temperature for 2 hours; the two solutions were mixed and stirred at room temperature for 2 hours to obtain a mixed colloidal solution, which was freeze-dried for 48 hours to obtain an A2-positive electrode fluorine-free binder (0.5α-HP / PVA / GL).

[0059] Example 3

[0060] The component ratio, preparation operation and process parameters of the positive electrode fluorine-free binder prepared in this embodiment are basically the same as those in Example 1, except that the heating ratio of keratin in this embodiment is 10%, 20%, 40%, 60%, 70%, 80% and 90%, respectively, to obtain A3-positive electrode fluorine-free binder (0.1α-HP / PVA / GL), A4-positive electrode fluorine-free binder (0.2α-HP / PVA / GL), A5-positive electrode fluorine-free binder (0.4α-HP / PVA / GL), A6-positive electrode fluorine-free binder (0.6α-HP / PVA / GL), A7-positive electrode fluorine-free binder (0.7α-HP / PVA / GL), A8-positive electrode fluorine-free binder (0.8α-HP / PVA / GL) and A9-positive electrode fluorine-free binder (0.9α-HP / PVA / GL).

[0061] At the same time, in order to verify the comprehensive performance of the positive electrode fluorine-free binder prepared in the above examples, the present application provides the following comparative examples for detailed description.

[0062] Comparative Example 1

[0063] The component ratio, preparation operation and process parameters of the B1-adhesive prepared in this comparative example are basically the same as those in Example 1, except that keratin is not added in this comparative example to prepare the B1-adhesive (PVA / GL).

[0064] Comparative Example 2

[0065] This comparative example uses conventional polyvinylidene fluoride (PVDF) as a comparison, which is recorded as B2-binder (PVDF).

[0066] In order to verify the structural characteristics of the positive electrode fluorine-free binder prepared in the example, the prepared binder was subjected to infrared spectroscopy test.

[0067] according to Figure 1 It can be seen that when polyvinyl alcohol (PVA), glycerol (GL), keratin (α-HP) and 0.3α-HP / PVA / GL were subjected to infrared testing, keratin (α-HP) was at ~3280cm -1 and 1526cm -1 The NH peak of amide generated by CN stretching and NH in-plane mixing is at ∼1650 cm -1 The corresponding C=O absorption peak is at 1224 cm -1 The peak of SO bond vibration indicates that α-HP is keratin. -1 The stretching vibration peak of -OH was observed at 2910 cm -1 and 1424cm -1 is the characteristic peak of CH bond; glycerol (GL) at 3300cm -1 A broad and strong -OH stretching vibration peak was observed at 3250 cm-1. After keratin was cross-linked with polyvinyl alcohol and glycerol (0.3α-HP / PVA / GL), the -OH vibration peak (~3250 cm-1) -1 ) moves to a lower wave number, and the C=O peak belonging to keratin (~1650cm -1 ) becomes broader, and the NH peak shifts from 1528 cm -1 Offset to 1536cm -1 , SO peak from 1224cm -1 Offset to 1238cm -1 These phenomena indicate that there are a large number of hydrogen bonds between keratin and polyvinyl alcohol and glycerol.

[0068] In order to verify the comprehensive performance of the positive electrode fluorine-free binder prepared in the embodiment, the following tests were performed:

[0069] Peel test:

[0070] Use a universal testing machine to test the bonding performance between the positive electrode active material layer and the current collector. First, use transparent tape to bond the electrode surface with a width as wide as the tape. Then peel off 5-10mm of the active material layer to expose the current collector. Clamp one end of the current collector to the mobile fixture of the universal testing machine, and clamp the other end with tape to the fixed fixture of the tensile machine. Use the testing machine to perform a 180° peeling with a stroke speed of 50mm / min, so that the mobile fixture peels at a uniform speed at the set speed.

[0071] according to Figure 2 It can be seen that the carbonyl groups in keratin interact strongly with the hydroxyl groups of polyvinyl alcohol and glycerol through hydrogen bonding to enhance the cohesive force. The adhesion of 0.3α-HP / PVA / GL and 0.5α-HP / PVA / GL is significantly higher than that of PVDF and PVA / GL, but the adhesion of 0.5α-HP / PVA / GL is lower than that of 0.3α-HP / PVA / GL, indicating that excessive keratin α-HP (α-HP content is 50%) cannot achieve better adhesion strength and mechanical strength, while an appropriate amount of keratin α-HP (α-HP content is 30%) combined with PVA and GL can construct a 3D hydrogen bond network, thereby effectively improving the adhesion strength and mechanical strength.

[0072] Electrochemical performance test:

[0073] The sulfur cathode was prepared as follows: Ketjen black and sulfur powder were mixed in a 1:4 mass ratio, placed in a hydrothermal reactor, and argon was introduced. The mixture was then reacted in a forced air oven at 155°C for 14 hours to produce Ketjen black-coated sulfur particles (KB / S). The Ketjen black-coated sulfur particles served as the active material, SuperP as the conductive additive, and the fluorine-free binder from Examples 1-2 served as the binder. The active material, conductive additive, and binder were mixed in a mass ratio of 7:2:1 using deionized water as the solvent to form a uniform slurry, which was then coated onto aluminum foil. The electrode was then dried in a vacuum oven at 80°C for 12 hours and cut into small discs with a diameter of 14 mm to serve as the sulfur cathode.

[0074] A button-type lithium-sulfur battery was assembled by dissolving 1M LiTFSI in a 1:1 volume ratio of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) in a mixed solvent containing 1.0% lithium nitrate (LiNO3) as the lithium-sulfur electrolyte, lithium sheets as symmetrical electrodes, porous polypropylene (Celgard 2500) as the separator, and CR 2032 stainless steel as the battery case.

[0075] according to Figure 3It can be seen that the AC impedance of 0.3α-HP / PVA / GL, 0.5α-HP / PVA / GL, PVDF, and PVA / GL before charge and discharge cycles was tested. The lithium-sulfur batteries prepared with the four binders showed a semicircle in the high-frequency region and a slant line in the low-frequency region. 0.3α-HP / PVA / GL and 0.5α-HP / PVA / GL showed small charge transfer impedance. The charge transfer impedance of the positive electrode made of PVDF and PVA / GL was 60Ω, indicating that the sulfur / conductive carbon / binder composite material in the positive electrode had good electrical contact and could form an excellent conductive path.

[0076] according to Figure 4 As can be seen, the AC impedance diagrams of 0.3α-HP / PVA / GL, 0.5α-HP / PVA / GL, PVDF, and PVA / GL after 100 charge-discharge cycles at 1C show that the charge transfer impedance of the four binders is significantly reduced due to sulfur activation, showing two semicircles and a diagonal line. The semicircles in the high-frequency region of the positive electrodes using 0.3α-HP / PVA / GL and 0.5α-HP / PVA / GL as binders are much smaller, which is related to the diffusion of lithium ions through the solid electrolyte interface layer (SEI layer). This indicates that the positive electrodes using keratin / polyvinyl alcohol and glycerol as binders have a stable solid electrolyte interface layer after cycling. In addition, the semicircles in the low-frequency region are related to the charge transfer impedance. The positive electrodes using keratin / polyvinyl alcohol and glycerol as binders show smaller semicircles and their charge transfer impedance is significantly lower than that of the positive electrodes using PVDF and PVA / GL as binders, indicating that the binders are conducive to the formation of effective conductive paths.

[0077] according to Figure 5 It can be seen that the battery cycle performance of 0.3α-HP / PVA / GL, 0.5α-HP / PVA / GL, PVDF, and PVA / GL at 2C was tested. The sulfur cathode prepared with PVDF as the binder showed a capacity of 268 mAh g after 400 cycles at 2C. -1 The sulfur cathode prepared with 0.3α-HP / PVA / GL as the binder exhibited a capacity of 424 mAh g after 400 cycles at 2C. -1 , and the performance of 0.5α-HP / PVA / GL is better than that of PVDF and PVA / GL.

[0078] In order to explore the specific effect of the ratio of α-HP and PVA / GL on the performance, the A1-positive electrode fluorine-free binder (0.3α-HP / PVA / GL), A2-positive electrode fluorine-free binder (0.5α-HP / PVA / GL), A3-positive electrode fluorine-free binder (0.1α-HP / PVA / GL), A4-positive electrode fluorine-free binder (0.2α-HP / PVA / GL), A5-positive electrode fluorine-free binder (0.4 Electrodes made of A6-positive electrode fluorine-free binder (0.6α-HP / PVA / GL), A7-positive electrode fluorine-free binder (0.7α-HP / PVA / GL), A8-positive electrode fluorine-free binder (0.8α-HP / PVA / GL), and A9-positive electrode fluorine-free binder (0.9α-HP / PVA / GL) were tested for electrochemical performance. The discharge capacity was tested at 2C for 400 times. The results are shown in Table 1:

[0079] Table 1 Test results of discharge capacity of positive electrode fluorine-free binder at 2C for 400 times

[0080]

[0081] As shown in Table 1, the adhesives with different keratin contents prepared in the examples of the present application, according to the discharge capacity results of 400 times at 2C, gradually increase with the increase in the amount of keratin added, and reach the optimum when the addition amount is 30%. However, as the addition amount continues to increase, the discharge capacity gradually decreases.

[0082] according to Figure 6 It can be seen that the battery cycle performance of 0.3α-HP / PVA / GL, 0.5α-HP / PVA / GL, PVDF, and PVA / GL at 0.1C was tested. The sulfur cathode prepared with PVDF as the binder showed a capacity of 710 mAh g after 35 cycles at 0.1C. -1 The sulfur cathode prepared with 0.3α-HP / PVA / GL as the binder exhibited a capacity of 857 mAh g after 35 cycles at 0.1C. -1 , while the cycling performance of 0.5α-HP / PVA / GL and PVA / GL were better than that of PVDF, but worse than that of 0.3α-HP / PVA / GL.

[0083] according to Figure 7 It can be seen that the battery with 0.3α-HP / PVA / GL binder as sulfur positive electrode has a discharge capacity of 981mAh g at current densities of 0.2C, 0.5C, 1C, 2C, 3C, 4C, and 5C (respectively). -1 , 816mAh g -1 , 679mAh g -1, 545mAh g -1 , 458mAh g -1 , 398mAh g -1 , 338mAh g -1 ) are better than PVDF, PVA / GL, and 0.5α-HP / PVA / GL, indicating that the sulfur cathode prepared with the binder 0.3α-HP / PVA / GL, in which the weight proportion of keratin accounts for 30% of the total mass, has better electrochemical stability. The sulfur cathode prepared with 0.3α-HP / PVA / GL as the binder also maintains excellent rate performance under gradually increasing current density.

[0084] Therefore, the fluorine-free positive electrode binder provided in this application is prepared by combining polyvinyl alcohol, glycerol, and keratin. The binder prepared in this application forms a binder network structure with enhanced cohesion through non-covalent hydrogen bonding, which can improve the mechanical properties and structural stability of the positive electrode. It has broad application prospects in lithium-sulfur batteries as a sulfur positive electrode material.

[0085] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0086] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A positive electrode fluorine-free binder, characterized in that By mass percentage, it is composed of the following components: Polyvinyl alcohol and glycerol 40-90%; Keratin 10-60%; The mass ratio of the polyvinyl alcohol to glycerol is 22:

3.

2. The positive electrode fluorine-free binder according to claim 1, characterized in that The mass percentage of the keratin is 20-50%.

3. The positive electrode fluorine-free binder according to claim 1, characterized in that The mass percentage of the keratin is 30%.

4. The positive electrode fluorine-free binder according to claim 1, characterized in that The molecular weight of the polyvinyl alcohol is 20-25 kDa, and the alcoholysis degree is 98-99% (mol / mol).

5. A method for preparing the positive electrode fluorine-free binder according to any one of claims 1 to 4, characterized in that: The preparation method comprises: The positive electrode fluorine-free binder is obtained by reacting keratin, polyvinyl alcohol and glycerol in water and then freeze-drying the reactants.

6. The method for preparing a positive electrode fluorine-free binder according to claim 4, wherein: The time for reacting keratin, polyvinyl alcohol and glycerin in water is 2-4 hours.

7. The method for preparing a positive electrode fluorine-free binder according to claim 4, wherein: The freeze-drying time is 36-48 hours.

8. Use of the positive electrode fluorine-free binder according to any one of claims 1 to 4 or the positive electrode fluorine-free binder prepared by the preparation method according to any one of claims 5 to 7 in preparing a sulfur positive electrode.

9. A sulfur cathode material, characterized in that The invention comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode fluorine-free binder, and the positive electrode fluorine-free binder is the positive electrode fluorine-free binder according to any one of claims 1 to 4.

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