Redox mediator functionalized binder as well as preparation method and application thereof

Abstract

The invention discloses a redox mediator functional binder for improving the low-temperature performance of a lithium iron phosphate battery and a preparation method of the redox mediator functional binder, and belongs to the technical field of lithium ion battery materials. The novel binder is a diblock polymer which integrates a ferrocene group and a polyoxyethylene-containing side chain. Wherein the ferrocene group is used as a redox mediator and can generate efficient reversible redox reaction at low temperature, and the oxidation state (ferrocene positive ions) of the ferrocene group can chemically oxidize Fe in the lithium iron phosphate, so that the limitation of slow intrinsic reaction kinetics of the material is avoided, and the electrode reaction is driven; meanwhile, the polyoxyethylene-containing side chain can optimize a lithium ion solvation structure at an electrode interface through a coordination effect between specific ether oxygen atoms and lithium ions, so that a desolvation energy barrier of the lithium ions at the interface is remarkably reduced, and the ion transmission rate is accelerated. According to the invention, the specific discharge capacity and rate capability of the lithium iron phosphate battery under a low-temperature condition can be greatly improved.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery cathode materials, specifically relating to a functionalized binder, its preparation method, and its application. The functionalized binder contains redox mediator groups, which can improve the Fe content of lithium iron phosphate at low temperatures through efficient redox reactions. 2+ / Fe 3+ The reaction kinetics significantly improve the low-temperature discharge capacity and rate performance of the battery. Background Technology

[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, possesses a high theoretical discharge specific capacity (170 mAh / g) and a stable discharge plateau (approximately 3.4 V vs. Li). + Lithium iron phosphate (LFP) materials possess advantages such as high efficiency (Li₂O₃ / Li₂O₃) and excellent thermal stability. Furthermore, under extreme conditions such as overcharging and short circuits, LFP materials are less prone to thermal runaway. Therefore, lithium-ion batteries using LFP as the active material exhibit good cycle stability, safety, and cost advantages, making them one of the most widely used cathode materials in the current power battery market, playing a crucial role in new energy vehicles, energy storage systems, and other fields.

[0003] However, lithium iron phosphate materials have a low intrinsic electronic conductivity (approximately 10). -9 (S / cm) and low lithium-ion diffusion coefficient (approximately 10) -14 The disadvantage of (cm² / s). Therefore, in low-temperature environments, Fe 2+ / Fe 3+ The redox reaction kinetics are significantly slowed down. Specifically, this manifests as a reduced migration rate of lithium ions in the one-dimensional diffusion channels of lithium iron phosphate, impeded electron transport between active particles, and increased charge transfer impedance at the cathode / electrolyte interface. These factors combined cause a sharp decline in the discharge specific capacity and rate performance of lithium iron phosphate batteries under low-temperature conditions, severely limiting their application in cold environments. To address these issues, existing technologies mainly focus on two directions: ① Cathode material modification, using techniques such as particle size reduction, surface carbon coating, element doping, and morphology control to increase reactive sites and shorten ion / electrolyte transport paths. ② Electrolyte optimization, reducing electrolyte viscosity and promoting the desolvation process of lithium ions at the cathode / electrolyte interface by developing low-freezing-point electrolytes, adding functional additives, and controlling the solvation structure. Nevertheless, these methods still have limitations: nano-sizing complicates the preparation process and significantly increases costs; nanoparticles are prone to agglomeration and have low tap density; surface coatings may hinder lithium-ion transport; doping modification has limited effect on improving the intrinsic electrochemical performance of the material; and electrolyte optimization strategies cannot fundamentally solve the problems of low intrinsic electronic conductivity and small ion diffusion coefficient in lithium iron phosphate materials, particularly for Fe...2+ / Fe 3+ The improvement in redox reaction kinetics is very limited.

[0004] In summary, none of the existing technical solutions for improving the low-temperature performance of lithium iron phosphate batteries address the lithium iron phosphate Fe content. 2+ / Fe 3+ The intrinsic potential barrier of redox reactions makes it difficult to achieve breakthrough improvements in low-temperature performance. Furthermore, material modification methods are complex, costly, and difficult to scale up for industrial production. Therefore, there is an urgent need to develop a new method that is simple in process, cost-controllable, and can effectively improve the low-temperature performance of lithium iron phosphate batteries to meet the application requirements of power batteries in cold environments. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a redox-mediated functionalized binder and its preparation method, which, when used in lithium iron phosphate cathodes, significantly improves the low-temperature performance of lithium iron phosphate batteries. The binder of this invention is a functionalized polymer integrating ferrocene groups and polyoxyethylene side chains. The ferrocene groups, acting as redox mediators, can undergo efficient reversible redox reactions at low temperatures, and their oxidized state (ferrocene cations) can chemically oxidize Fe in lithium iron phosphate. 2+ This bypasses the limitation of slow intrinsic reaction kinetics of the material, driving the electrode reaction. Simultaneously, the polyoxyethylene-containing side chains, through their unique coordination between ether oxygen atoms and lithium ions, optimize the lithium-ion solvation structure at the electrode interface, significantly reducing the desolvation energy barrier at the interface and accelerating ion transport rates. When this binder is used in lithium iron phosphate cathode materials, it not only achieves conventional bonding functions but also simultaneously improves the low-temperature reaction kinetics of the lithium iron phosphate cathode from two key aspects: electron transport and ion transport. This significantly enhances the battery's discharge specific capacity and rate performance under low-temperature conditions.

[0006] The objective of this invention is achieved through the following technical solution: the redox mediator functionalized binder and its specific preparation method include the following steps: Step 1: In a Schleck reaction flask, sequentially add methoxy polyoxyethylene acrylate or its derivatives (molecular formula CH3O(-C2H4-O)n-CO-C(R1)=CH2) as monomers, RAFT reagents (ethyl-2-formyl-2-phenylbutyrate or 4-cyano-4-(thiobenzoyl)valerate or 2-(dodecyltrithiocarbonate)-2-methylpropionic acid or 2,2'-(thiocarbonylbis(thioalkyldiyl))bis(2-methylpropionic acid)), initiator (AIBN or BPO), and anhydrous solvent (solvent is toluene or tetrahydrofuran or a mixture of both in any proportion, in an amount 10-30 times the volume of the reactants). The molar ratio of monomer to RAFT reagent is 50:1 to 500:1, the amount of initiator is 0.1-0.5 times the mass of RAFT reagent, and the amount of solvent is 10-30 times the volume of the reactants. The reaction system is purged with a protective gas, and the process is repeated 3-5 times using a cycle of freezing, vacuuming, and purging to ensure the system is anhydrous and oxygen-free. A magnetic stirrer is then activated to completely dissolve the raw materials. The temperature is raised to 60-90°C for polymerization. After 2-12 hours of reaction, the reaction solution is added dropwise to a precipitant (methanol or n-hexane, or a mixture of both in any proportion, at a volume 2-5 times the solvent volume) to precipitate the polymer. The precipitate is collected by filtration, washed 3-5 times with the precipitant, and dried under vacuum to constant weight to obtain the first block polymer. R1 is one of H, CH3, C2H5, C3H7, or C4H9, n = 4-12, and x = 50-500.

[0007]

[0008] Step 2: Add the first block polymer as a macromolecular RAFT reagent and vinyl ferrocene or its derivative as a monomer to an anhydrous solvent (solvent is toluene or tetrahydrofuran or a mixture of the two in any proportion, the amount being 10-30 times the volume of the reactants). The molar ratio of vinyl ferrocene to the first block polymer is 50:1 to 500:1, which can be determined according to the target block length. Add an appropriate amount of initiator (AIBN or BPO, approximately 0.1-0.5 times the mass of the first block polymer). Purge the reaction system with a protective gas, and cycle through freezing-vacuuming-gas 3-5 times to ensure the reaction system is anhydrous and oxygen-free. Raise the temperature to 60-90℃ for chain extension reaction. After reacting for 2-12 hours, drop the reaction solution into a precipitant (methanol or n-hexane or a mixture of the two in any proportion, the amount being 2-5 times the volume of the solvent), filter to collect the product, wash several times with the precipitant, and vacuum dry to constant weight to obtain the AB diblock copolymer (denoted as PVF-). b -MPEG). R2 is one of H, CH3, C2H5, C3H7, C4H9. R2 and R1 can be the same or different. y = 50-500, x:y = 1:1~1:9.

[0009]

[0010] Preferably, the RAFT reagent in step one is one of ethyl-2-formyl-2-phenylbutyrate, 4-cyano-4-(thiobenzoyl)valerate, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, and 2,2'-(thiocarbonylbis(thioalkyldiyl))bis(2-methylpropionic acid), and the amount used is 1 / 50 to 1 / 500 of the monomer; Preferably, the anhydrous solvent in steps one and two is toluene or tetrahydrofuran or a mixture of the two in any proportion, and the amount used is 10-30 times the volume of the corresponding reactants. The solvent amount ratio in steps one and two can be the same or different. Preferably, the molar ratio of reactant monomers to RAFT reagents in steps one and two is in the range of 50:1 to 500:1. This ratio can be the same or different in steps one and two. Preferably, the amount of initiator used in steps one and two is 0.1-0.5 times the mass of the RAFT reagent. The ratio of the amount of initiator used in steps one and two can be the same or different. Preferably, the protective gas used in steps one and two is one of N2 / He / Ar or a mixture of multiple gases in any proportion. The protective gases used in steps one and two can be the same or different. Preferably, the product precipitant in steps one and two is methanol or n-hexane or a mixture of the two in any proportion, and the amount used is 2-5 times the volume of the solvent. This proportion can be the same or different in steps one and two. Another objective of this invention is to provide a redox-mediated binder prepared by the above method, which has good redox driving and bonding properties.

[0011] Another objective of this invention is to provide the low-temperature application of the aforementioned redox mediator binder in lithium iron phosphate batteries.

[0012] Compared with existing technologies, the novel redox mediator binder prepared by the technology provided in this invention has the following advantages and beneficial effects: (1) The novel binder synthesized in this invention contains ferrocene groups as a redox mediator, which can undergo efficient reversible redox reactions at low temperatures (-20℃, -30℃, -40℃). Its oxidized state (ferrocene cation) can chemically oxidize Fe in lithium iron phosphate. 2+ This bypasses the limitation of slow intrinsic reaction kinetics of materials and drives the electrode reaction.

[0013] (2) The novel binder synthesized in this invention contains polyoxyethylene side chains. Through the coordination between its unique ether oxygen atoms and lithium ions, it optimizes the lithium ion solvation structure at the electrode interface, significantly reduces the desolvation energy barrier of lithium ions at the interface, accelerates lithium ion transport, and forms a highly efficient synergistic effect with ferrocene.

[0014] (3) The redox medium binder proposed in this invention has strong adhesion and can effectively improve the low-temperature electrochemical performance of lithium iron phosphate batteries (when LFP batteries are assembled using the binder prepared in this invention, discharge specific capacities of 116.07 mAh / g, 97.14 mAh / g and 74.02 mAh / g can be obtained at -20℃, -30℃ and -40℃, respectively). It is suitable for the current commercial lithium-ion battery production equipment and processes and can realize industrial-scale production. Attached Figure Description

[0015] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0016] Figure 1 The redox-mediated functionalized binder (PVF-) prepared in Example 1 b (a) Infrared absorption spectrum and (b) NMR spectrum of MPEG.

[0017] Figure 2 The PVF prepared in Example 1 b -The intrinsic (a) cycling performance and (b) charge-discharge curves of MPEG binder as a redox medium.

[0018] Figure 3 Based on the PVF prepared in Example 1 b -MPEG binder to prepare the surface microstructure of lithium iron phosphate composite electrodes.

[0019] Figure 4 The PVF prepared in Example 1 b -MPEG, Lithium Iron Phosphate (Example 1 PVF- b CV comparison curves of -MPEG binder and lithium iron phosphate (comparative example 1 PVDF binder) at 25℃.

[0020] Figure 5 Based on Example 1 PVF- b CV comparison curves of lithium iron phosphate electrodes prepared with -MPEG binder at 25℃ and -20℃.

[0021] Figure 6 Based on Example 1 PVF- b- Comparison of AC impedance of lithium iron phosphate batteries prepared with MPEG binder and PVDF binder in Comparative Example 1.

[0022] Figure 7 The PVF- prepared in Example 1 was used respectively. b -The specific discharge capacity of lithium iron phosphate batteries using PVDF as binder in MPEG and Comparative Example 1 at low temperatures (-20℃, -30℃, -40℃). Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Example 1

[0024] This embodiment provides a method for preparing a redox-mediated functionalized binder, comprising the following steps: Step 1: In a Schleck reaction flask, add the monomer CH3O(-C2H4-O)5-CO-CH=CH2, the RAFT reagent 4-cyano-4-(thiobenzoyl)valerate, the initiator AIBN, and anhydrous toluene solvent sequentially. The molar ratio of monomer to RAFT reagent is 100:1, the amount of initiator is 0.2 times the mass of RAFT reagent, and the amount of solvent is 20 times the volume of reactants. Purge the reaction system with nitrogen, and cycle through freezing-vacuuming-nitrogen purging five times to ensure the reaction system is anhydrous and oxygen-free. Turn on the magnetic stirrer to completely dissolve the raw materials, and heat to 70°C for polymerization. After 6 hours of reaction, slowly add the reaction solution dropwise to methanol (volume 2.5 times the volume of the reaction solvent) to precipitate the polymer. Filter and collect the precipitate, wash it 3-5 times with methanol, and then vacuum dry it to constant weight to obtain the first block polymer (x=100).

[0025] Step 2: The first block polymer was used as a macromolecular RAFT reagent, and vinyl ferrocene was used as a monomer in anhydrous toluene (solvent volume was 20 times the volume of the reactants). The molar ratio of vinyl ferrocene to the first block polymer was 100:1. Then, an appropriate amount of initiator AIBN (0.2 times the mass of the first block polymer) was added. The reaction system was purged with nitrogen, and the reaction was cycled through freezing-vacuuming-nitrogen purging five times to ensure the reaction system was anhydrous and oxygen-free. The chain extension reaction was carried out at 60°C. After 4 hours of reaction, the reaction solution was added dropwise to precipitate in methanol (volume was 2.5 times the volume of the reaction solvent), causing the polymer to precipitate. The precipitate was collected by filtration, washed 3-5 times with methanol, and then vacuum dried to constant weight to obtain the AB diblock copolymer (y=100), which was named PVF- b -MPEG.

[0026] Figure 1The redox mediator functionalized binder PVF- prepared in this embodiment b -MPEG's infrared absorption spectrum and proton nuclear magnetic resonance spectrum, from Figure 1 a indicates that the characteristic peak of vinyl groups is at 1625 cm⁻¹. -1 It completely disappeared after the polymerization reaction and at 1680 cm⁻¹ -1 A distinct new peak appeared, corresponding to the infrared absorption peak of ethyl, indicating that the polyacrylate containing the (-C2H4-O)5 side chain prepared in step one was successfully polymerized onto vinyl ferrocene. Figure 1 b also indicates the disappearance of the double bonds in polyvinyl ferrocene and methoxy polyoxyethylene acrylate, and the appearance of a broad peak in vinyl groups, indicating that block copolymerization has occurred. Cyclic charge-discharge tests were performed on this polymer. Figure 2 (a) Its first-cycle discharge specific capacity is approximately 104 mAh g. -1 After 5 cycles, it gradually stabilized at 70 mAh g. -1 And even after 78 cycles, it still has nearly 60 mAh g. -1 Furthermore, the coulombic efficiency is as high as 98.6%, indicating that the material has good stability. Figure 2 (b) Comparison of charge-discharge curves with different number of cycles revealed that the redox mediator functionalized binder has a clear charge-discharge plateau during charge-discharge, which also indicates that this material is used in LFP electrode materials.

[0027] The AB diblock copolymer prepared in this embodiment is used as a binder (PVF- b Performance testing of MPEG application in lithium iron phosphate cathode: The obtained AB diblock copolymer PVF- b MPEG, conductive carbon, and lithium iron phosphate powder were mixed evenly in anhydrous NMP solvent at a mass ratio of 1:1:8 and stirred continuously at 500 r / min for 12 h to form a "yogurt-like" slurry. The slurry was then evenly coated onto a 20 μm thick aluminum foil using a scraper. The foil was first dried in a forced-air drying oven at 60℃ for 2-3 h, then vacuum dried in a vacuum drying oven at 80℃ for 12 h. Finally, it was cut into circular electrode sheets with a diameter of 12 mm, weighed, and stored in a glove box for later use. The active material loading of the electrode sheets was approximately 4.2 mg / cm³. 2 . Figure 3 The PVF- prepared based on this embodiment b The surface morphology of the lithium iron phosphate electrode prepared by the -MPEG binder shows that the solid particles are all adhered to the binder, and the overall morphology is uniform, indicating that the binder can evenly and tightly bond the lithium iron phosphate particles and conductive carbon together.

[0028] A 2032 coin cell was assembled using a self-made lithium iron phosphate electrode as the positive electrode, a commercial lithium sheet (15.6 mm in diameter and 0.45 mm thick) as the negative electrode, a PP film as the separator, and 1 mol / L LiPF6 (EC / PC = 1:1, V / V) as the electrolyte. Performance testing was conducted after the battery was allowed to stand at room temperature for 4 hours following assembly. PVF- b -MPEG performs CV testing ( Figure 4 The redox peaks of lithium iron phosphate (with PVDF as binder, molecular weight 400,000-600,000) were found to be at 3.35 V and 3.18 V, respectively. The redox peaks of lithium iron phosphate (with PVDF as binder, molecular weight 400,000-600,000) were at 3.59 V and 3.28 V. Replacing the binder with PVDF... b During the -MPEG test, the lithium iron phosphate electrode exhibits two sets of redox peaks: 3.51 V and 3.35 V correspond to the redox peaks of lithium iron phosphate, and 3.32 V and 3.24 V correspond to the redox peaks of PVF-. b -MPEG redox peak. When the temperature drops to -20℃ ( Figure 5 The reduction peaks of the two almost overlap at 3.08 V, while the oxidation peaks change to 3.48 V and 3.71 V, respectively, indicating that -20°C can trigger PVF- b - The redox mediating effect of MPEG binder. AC impedance testing shows that the interfacial impedance of Li|LFP cells using traditional PVDF binders is approximately 248 Ω, while that using redox mediator binders with PVDF-... b -MPEG's Li|LFP cell has an interface impedance of only 201 Ω, a decrease of 47 Ω, demonstrating superior interface ion transport capability. Figure 6 At 0.1°C, for use with PVF- b -Li|LFP batteries with MPEG as binder undergo low-temperature discharge testing. Figure 7 Its discharge curves at -20℃, -30℃, and -40℃ are based on PVF- b The discharge plateaus of the LFP batteries based on MPEG are 3.24 V, 3.19 V, and 2.98 V, showing a clear discharge voltage plateau. In contrast, the discharge plateaus of the LFP batteries based on PVDF are 3.19 V, 3.05 V, and 2.82 V, significantly lower than those based on PVDF. b -MPEG indicates PVF- b -MPEG can improve the reaction kinetics rate of LFP batteries at low temperatures, thereby reducing battery polarization. (The last part, "-MPEG," appears to be an incomplete sentence fragment and doesn't translate directly. It likely refers to a specific technology or application, possibly related to PVF-based technology, but without further context, a precise translation isn't possible.) bThe discharge specific capacities of the LFP battery based on MPEG were 116.07 mAh / g, 97.14 mAh / g, and 74.02 mAh / g, respectively, significantly better than those of the PVDF-based LFP battery (107.66 mAh / g, 72.14 mAh / g, and 56.37 mAh / g). Furthermore, the discharge specific capacities showed a trend of increasing with lower temperatures, resulting in higher discharge capacities for PVDF-based LFP batteries. b The more pronounced the effect of MPEG, the better. This further reflects the effect of PVF- b -MPEG has a good effect on improving the low-temperature performance of LFP batteries. Example 2

[0029] Step 1: In a Schleck reaction flask, add the monomer CH3O(-C2H4-O)4-CO-C(CH3)=CH2, the RAFT reagent 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, the initiator AIBN, and anhydrous toluene solvent sequentially. The molar ratio of monomer to RAFT reagent is 200:1, the amount of initiator is 0.3 times the mass of RAFT reagent, and the amount of solvent is 20 times the volume of reactants. Purge the reaction system with nitrogen, and cycle through freezing-vacuuming-nitrogen purging five times to ensure the reaction system is anhydrous and oxygen-free. Turn on the magnetic stirrer to completely dissolve the raw materials, and heat to 90°C for polymerization. After 2 hours of reaction, slowly add the reaction solution dropwise to n-hexane (volume 3 times the volume of the reaction solvent) to precipitate the polymer. Filter and collect the precipitate, wash it 3-5 times with methanol, and then vacuum dry it to constant weight to obtain the first block polymer (x=200).

[0030] Step 2: The first block polymer was used as the macromolecular RAFT reagent, and C2H5-CH=CH(C5H4)Fe(C5H5) was used as the monomer, added to anhydrous toluene (the solvent volume was 30 times the volume of the reactants). The molar ratio of vinylferrocene to the first block polymer was 300:1. Then, an appropriate amount of initiator AIBN (0.3 times the mass of the first block polymer) was added. The reaction system was purged with helium, and the reaction was cycled through freezing, vacuuming, and nitrogen purging five times to ensure anhydrous and oxygen-free conditions. The chain extension reaction was carried out at 60°C. After 12 hours of reaction, the reaction solution was added dropwise to methanol (3 times the volume of the reaction solvent) to precipitate the polymer. The precipitate was collected by filtration, washed 3-5 times with n-hexane, and then vacuum dried to constant weight to obtain the AB diblock copolymer (y=300).

[0031] The AB diblock copolymer obtained above was used as a binder in the lithium iron phosphate cathode. The electrode preparation and battery assembly were the same as in Example 1. The low-temperature performance of the battery was tested. The corresponding initial voltages at 0.1 C discharge at -20℃, -30℃, and -40℃ were 3.22 V, 3.16 V, and 2.95 V, respectively. The discharge voltage plateaus were obvious, at 3.13 V, 3.00 V, and 2.87 V, respectively, indicating that the voltage was relatively stable during the low-temperature discharge process. The battery discharge specific capacity was 103.11 mAh / g at -20℃ and 95.89 mAh / g at -30℃. When the temperature was reduced to -40℃, the discharge specific capacity was still 80.92 mAh / g. Example 3

[0032] Step 1: In a Schleck reaction flask, add the monomer CH3O(-C2H4-O)4-CO-C(C2H5)=CH2, the RAFT reagent ethyl-2-formyl-2-phenylbutyrate, the initiator BPO, and anhydrous toluene solvent sequentially. The molar ratio of monomer to RAFT reagent is 150:1, the amount of initiator is 0.2 times the mass of RAFT reagent, and the amount of solvent is 20 times the volume of reactants. Purge the reaction system with nitrogen, and cycle through freezing-vacuuming-nitrogen purging five times to ensure the reaction system is anhydrous and oxygen-free. Turn on the magnetic stirrer to completely dissolve the raw materials, and heat to 75°C for polymerization. After 4 hours of reaction, slowly add the reaction solution dropwise to methanol (volume 2.5 times the volume of the reaction solvent) to precipitate the polymer. Filter and collect the precipitate, wash it 3-5 times with methanol, and then vacuum dry it to constant weight to obtain the first block polymer (x=150).

[0033] Step 2: The first block polymer was used as a macromolecular RAFT reagent, and C3H7-CH=CH(C5H4)Fe(C5H5) was added as a monomer to tetrahydrofuran (the solvent volume was 20 times the volume of the reactants). The molar ratio of vinylferrocene to the first block polymer was 200:1. Then, an appropriate amount of initiator BPO (0.25 times the mass of the first block polymer) was added. The reaction system was purged with nitrogen, and the reaction was cycled through freezing, vacuuming, and nitrogen purging five times to ensure anhydrous and oxygen-free conditions. The chain extension reaction was carried out at 80°C. After 6 hours of reaction, the reaction solution was added dropwise to a precipitant, methanol (2.5 times the volume of the reaction solvent), to precipitate the polymer. The precipitate was collected by filtration, washed 3-5 times with methanol, and then vacuum dried to constant weight to obtain the AB diblock copolymer (y=200).

[0034] The AB diblock copolymer obtained above was used as a binder in the lithium iron phosphate cathode. The electrode preparation and battery assembly were the same as in Example 1. The low-temperature performance of the battery was tested. The corresponding initial voltages at 0.1 C discharge at -20℃, -30℃, and -40℃ were 3.21 V, 3.13 V, and 2.90 V, respectively. The discharge voltage plateaus were obvious, at 3.15 V, 3.02 V, and 2.78 V, respectively, indicating that the voltage was relatively stable during the low-temperature discharge process. The battery discharge specific capacity was 104.45 mAh / g at -20℃ and 96.71 mAh / g at -30℃. When the temperature was reduced to -40℃, the discharge specific capacity was still 80.94 mAh / g.

[0035] Examples 4-10 The CH3O(-C2H4-O) in step one of Example 1 n The polymerization degree n of -CO-CR1=CH2 was replaced with 4, 6, 7, 8, 9, 11, and 12, respectively, and R1 was replaced with CH3, C2H5, C3H7, C4H9, CH3, C2H5, and C3H7, respectively. In step two, R2 in R2CH=CH(C5H4)Fe(C5H5) was replaced with CH3, C2H5, C3H7, C4H9, C3H7, C4H9, and CH3, respectively. The other preparation process was the same as in Example 1. A binder with redox mediator function was obtained, and Li|LFP batteries were assembled and tested. The low-temperature performance of the batteries assembled in Examples 4-10 is shown in Table 1.

[0036] Table 1. Low-temperature performance of the binder-assembled batteries with redox mediator functions prepared in Examples 4-10

[0037] Note: Discharge voltage is in V, and discharge specific capacity is in mAh / g. Examples 11-14 The monomer polymerization degrees x and y in steps one and two of Example 1 were adjusted to those shown in Table 2. The other preparation processes were the same as in Example 1 to obtain a binder with redox mediator function. Li|LFP batteries were then assembled and tested. The low-temperature performance of the batteries assembled in Examples 11-14 is shown in Table 1.

[0038] Table 2. Low-temperature performance of the binder-assembled batteries with redox mediator functions prepared in Examples 11-14

[0039] Note: Discharge voltage is in V, and discharge specific capacity is in mAh / g. Comparative Example 1 The binder in Example 1 was replaced with commercial PVDF (molecular weight 400,000-600,000), and its discharge curves at -20℃, -30℃, and -40℃ are shown below. Figure 7 As shown, at temperatures of -20℃ and -30℃, the discharge plateau voltages were 3.19 V and 3.05 V, respectively, showing a significant decrease. The discharge specific capacity at 0.1 C was only 97.14 mAh / g and 74.02 mAh / g, respectively. When the temperature dropped to -40℃, the initial discharge voltage was only 2.82 V, and the discharge specific capacity at 0.1 C was only 56.37 mAh / g. The initial discharge voltage, voltage plateau, and discharge specific capacity were all significantly lower than those in Examples 1 and 2-16, indicating that the low-temperature performance of the redox-mediated functionalized binder prepared in this invention is significantly superior to that of commercial PVDF binders.

[0040] Comparative Example 2 The binder in Example 1 was replaced with commercially available PEO (molecular weight 10). 6 The battery exhibits a low initial voltage of 3.01 V when discharging at -20℃, followed by a significant drop in discharge plateau voltage to only 2.79 V, and a discharge specific capacity of only 38.15 mAh / g at 0.1 C. When the temperature drops to -30℃ and -40℃, the initial voltages are only 2.70 V and 2.59 V respectively, with almost no discharge voltage plateau, and the voltage rapidly drops to the cutoff voltage (2.5 V). The discharge specific capacity at 0.1 C is <10 mAh / g, indicating that it only maintains inefficient operation at -20℃. At further temperature drops to -30℃ and -40℃, the battery is almost inoperable. This demonstrates that the low-temperature performance of the binder prepared in this invention is significantly superior to that of commercial PEO binders.

[0041] Comparative Example 3 The adhesive in Example 1 was replaced with commercial PAA (molecular weight 10). 5 -10 6 The adhesive, when discharged at -20℃ and -30℃, exhibits initial voltages of 3.11 V and 2.93 V, respectively, with significant drops in discharge plateau voltage to only 2.71 V and 2.62 V. When the temperature drops to -40℃, the discharge specific capacity at 0.1 C is only 31.56 mAh / g and 16.51 mAh / g, respectively. The initial voltage is only 2.64 V, with almost no discharge voltage plateau, and the voltage rapidly drops to the cutoff voltage (2.5 V). The discharge specific capacity at 0.1 C is <10 mAh / g, indicating that the low-temperature performance of the adhesive prepared in this invention is significantly superior to that of commercial PAA adhesives.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution with reference to preferred embodiments of the present invention, and are not intended to limit it. The embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered as equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. The objective of this invention is achieved through the following technical solution: the redox mediator functionalized binder and its specific preparation method include the following steps: Step 1: In a Schleck reaction flask, sequentially add methoxy polyoxyethylene acrylate or its derivatives (molecular formula CH3O(-C2H4-O)n-CO-C(R1)=CH2) as monomers, RAFT reagents (ethyl-2-formyl-2-phenylbutyrate or 4-cyano-4-(thiobenzoyl)valerate or 2-(dodecyltrithiocarbonate)-2-methylpropionic acid or 2,2'-(thiocarbonylbis(thioalkyldiyl))bis(2-methylpropionic acid)), initiator (AIBN or BPO), and anhydrous solvent (solvent is toluene or tetrahydrofuran or a mixture of both in any proportion, in an amount 10-30 times the volume of the reactants). The molar ratio of monomer to RAFT reagent is 50:1 to 500:1, the amount of initiator is 0.1-0.5 times the mass of RAFT reagent, and the amount of solvent is 10-30 times the volume of the reactants. The reaction system is purged with a protective gas, and the process is repeated 3-5 times using a cycle of freezing, vacuuming, and purging to ensure the system is anhydrous and oxygen-free. A magnetic stirrer is then activated to completely dissolve the raw materials. The temperature is raised to 60-90°C for polymerization. After 2-12 hours of reaction, the reaction solution is added dropwise to a precipitant (methanol or n-hexane, or a mixture of both in any proportion, at a volume 2-5 times the solvent volume) to precipitate the polymer. The precipitate is collected by filtration, washed 3-5 times with the precipitant, and then vacuum-dried to constant weight to obtain the first block polymer. R1 is one of H, CH3, C2H5, C3H7, C4H9, n=4-12, x=50-500; ； Step 2: Add the first block polymer as a macromolecular RAFT reagent and vinyl ferrocene or its derivative as a monomer to an anhydrous solvent (solvent is toluene or tetrahydrofuran or a mixture of the two in any proportion, the amount being 10-30 times the volume of the reactants). The molar ratio of vinyl ferrocene to the first block polymer is 50:1 to 500:1, which can be determined according to the target block length. Add an appropriate amount of initiator (AIBN or BPO, approximately 0.1-0.5 times the mass of the first block polymer). Purge the reaction system with a protective gas, and cycle through freezing-vacuuming-gas 3-5 times to ensure the reaction system is anhydrous and oxygen-free. Raise the temperature to 60-90℃ for chain extension reaction. After reacting for 2-12 hours, drop the reaction solution into a precipitant (methanol or n-hexane or a mixture of the two in any proportion, the amount being 2-5 times the volume of the solvent), filter to collect the product, wash several times with the precipitant, and vacuum dry to constant weight to obtain the AB diblock copolymer (denoted as PVF-). b -MPEG). R2 is one of H, CH3, C2H5, C3H7, C4H9. R2 and R1 can be the same or different. y = 50-500, x:y = 1:1~1:9; 2. In step one, the RAFT reagent is one of ethyl-2-formyl-2-phenylbutyrate, 4-cyano-4-(thiobenzoyl)valerate, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, or 2,2'-(thiocarbonylbis(thioalkyldiyl))bis(2-methylpropionic acid), and the amount used is 1 / 50 to 1 / 500 of the monomer.

3. In steps one and two, the anhydrous solvent is toluene or tetrahydrofuran or a mixture of the two in any proportion, and the amount used is 10-30 times the volume of the corresponding reactants. The solvent ratio in steps one and two can be the same or different.

4. Preferably, the molar ratio of reactant monomers to RAFT reagents in steps one and two is in the range of 50:1 to 500:

1. This ratio can be the same or different in steps one and two.

5. Preferably, the amount of initiator used in steps one and two is 0.1-0.5 times the mass of the RAFT reagent. The amount and ratio of initiator used in steps one and two can be the same or different.

6. Preferably, the protective gas in steps one and two is one of N2 / He / Ar or a mixture of multiple gases in any proportion. The protective gases used in steps one and two can be the same or different.

7. Preferably, the precipitant for the product in steps one and two is methanol or n-hexane or a mixture of the two in any proportion, and the amount used is 2-5 times the volume of the solvent. This proportion can be the same or different in steps one and two.

8. A redox-mediated binder, characterized in that: The product is obtained by the preparation method described in any one of claims 1-8 and has good redox driving function and bonding properties.

9. The low-temperature application of the redox mediator binder of claim 8 in lithium iron phosphate batteries.

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