High-voltage positive electrode binder with multi-function synergy and preparation method and application thereof

Abstract

The invention discloses a high-voltage positive electrode binder with multiple synergistic functions as well as a preparation method and application of the high-voltage positive electrode binder. The invention provides a novel polymer for a high-voltage positive electrode, the main chain of the polymer has a three-dimensional network structure, and the molecular structure contains cyano (-CN) and carbonyl (C = O) functional groups. The polymer integrating three core functions of high-strength adhesion, transition metal ion migration inhibition and interface stability regulation and control is obtained through accurate design of a molecular structure, shows excellent comprehensive performance, can be used as a high-voltage positive electrode binder, is applied to a high-voltage lithium ion battery system, shows breakthrough performance advantages, and has wide application prospects. The cycle life is remarkably prolonged, the rate capability is excellent, and the stability is excellent. In addition, the polymer also has excellent electrostatic spinning characteristics, and can be used for preparing a nanofiber membrane, and active substances are uniformly loaded in a network of the nanofiber membrane, so that an integrated solid-state positive electrode material is constructed.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-voltage positive electrode binder with multiple synergistic functions, its preparation method, and its application. Background Technology

[0002] The ever-growing demand for electric vehicles and the rapid depletion of lithium-ion batteries (LIBs) necessitate high energy density and resource sustainability in LIBs. The former requires the use of high-capacity electroactive materials maximized within a fixed electrode volume, while the latter essentially creates a closed-loop cycle for electroactive materials. In all these respects, binders are of practical significance in bonding electroactive materials, maintaining electrode integrity, and separating electrode slurry from the current collector. Currently, the crucial role of binders in enhancing the electrochemical behavior of sustainable high-capacity electroactive materials is recognized.

[0003] Polyvinylidene fluoride (PVDF) is a traditional polymer binder that has been widely used as a commercial binder for lithium-ion batteries due to its good electrochemical stability. However, some of its inherent properties, such as poor adhesion, low mechanical flexibility, and brittleness, often lead to cracking, breakage, or even pulverization during cycling, especially in materials with high theoretical capacity and significant volume changes. Advanced polymer binders must not only possess basic functions such as strong adhesion and excellent mechanical properties to maintain electrode integrity, but also be equipped with new functions, such as electronic and ionic conductivity and self-healing properties, to improve energy / power density, cycle life, and rate performance.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a novel polymer that possesses three core functions: high-strength adhesion, inhibition of transition metal ion migration, and regulation of interface stability, as well as excellent electrospinning properties. It can be used as a high-voltage cathode binder in high-voltage lithium-ion battery systems, demonstrating groundbreaking performance advantages.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a polymer for a high-voltage positive electrode, poly(4-cyanobutyl methacrylate) (PCM), having the general structural formula shown in Formula I:

[0007] In Formula I, n ranges from 150 to 300; the degree of polymerization ranges from 150 to 300.

[0008] In one specific embodiment of the present invention, the degree of polymerization of the polymer is 190.

[0009] Secondly, the present invention also provides a method for preparing the above-mentioned polymer, comprising the following steps: S1, 4-cyanobutyric acid reacts with oxalyl chloride to form 4-cyanobutyric acid chloride; S2. The obtained 4-cyanobutyric acid chloride undergoes an esterification reaction with vinyl alcohol to obtain 4-cyanobutyric acid vinyl ester monomer; S3. The obtained 4-cyanobutyric acid vinyl ester monomer undergoes RAFT polymerization to obtain the target product.

[0010] In step S1, the molar ratio of 4-cyanobutyric acid to oxaloyl chloride is 1:(1.1-2.0). The catalyst used in the acyl chloride reaction is N,N-dimethylformamide; The conditions for the acyl chloride reaction are: temperature 20-30℃, time 5-6h.

[0011] As a specific embodiment of the present invention, the reaction is carried out according to the following operation: 4-cyanobutyric acid is dissolved in ultra-dry dichloromethane, oxalyl chloride is added dropwise, a catalyst is added, the reaction is carried out at room temperature, and then purified by dichloromethane dissolution-rotary evaporation to obtain 4-cyanobutyric acid chloride.

[0012] In step S2, the molar ratio of 4-cyanobutyric acid to vinyl alcohol is 1:(1-1.2). The catalyst used in the esterification reaction is triethylamine; The conditions for the esterification reaction are: temperature 0-10℃ and time 5-6h.

[0013] In one specific embodiment of the present invention, the esterification reaction is carried out as follows: 4-cyanobutyric acid chloride is dissolved in dichloromethane and then added dropwise to a dichloromethane solution containing vinyl alcohol and triethylamine under ice bath conditions. After the esterification reaction is completed, the product is purified by column chromatography to obtain 4-cyanobutyric acid vinyl ester monomer. The neutral environment of the reaction system is maintained by using triethylamine to neutralize the HCl generated during the reaction, thereby promoting the smooth progress of the esterification reaction and increasing the yield.

[0014] In step S3, the initiator used in the RAFT polymerization reaction is 2,2-azobis(2-methylpropanediamine) dihydrochloride, and its amount is 0.01-0.1% of the molar amount of the 4-cyanobutyrate monomer; The RAFT reagent used in the RAFT polymerization reaction is 4-cyano-4-(thiobenzoylthio)pentanoic acid, and its amount is 0.005-0.05% of the molar amount of the 4-cyanobutyrate vinyl ester monomer; The conditions for RAFT polymerization are: pH of the reaction system is 4.0-6.0, temperature is 60-80℃, and time is 5-6h.

[0015] Further, step S3 also includes purification of the reaction product; the purification includes: washing the reaction product with water 3-5 times to remove acidic impurities, recrystallizing it 2-3 times with an acetonitrile / water mixed solvent, and then eluting it using silica gel column chromatography gradient; the volume ratio of acetonitrile to water in the mixed solvent is 1:(0.5-2); the eluent in the silica gel column chromatography gradient elution is composed of dichloromethane and methanol; the volume ratio gradient of dichloromethane to methanol varies in the range of (3-15):1.

[0016] Thirdly, the present invention also provides a positive electrode material comprising: a positive electrode active material, a conductive agent, and a binder; wherein the binder is the aforementioned polymer.

[0017] The positive electrode active material is selected from one or more of nickel-rich layered oxides, high-voltage lithium cobalt oxide, and lithium-rich manganese-based materials; the conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, and graphene; in the positive electrode material, the mass fraction of the binder is 3-10 wt%.

[0018] The polymer provided by this invention also has electrospinning properties, and nanofiber membranes can be prepared by electrospinning process.

[0019] Fourthly, the present invention also provides an integrated solid-state cathode material, comprising a nanofiber membrane and a cathode active material loaded thereon; the nanofiber membrane is prepared by electrospinning the above-mentioned polymer; the cathode active material is uniformly loaded into the fiber network structure of the nanofiber membrane by spraying technology.

[0020] Fifthly, the present invention also provides a positive electrode sheet, which is made using the above-mentioned positive electrode material.

[0021] In a sixth aspect, the present invention also provides a lithium-ion battery, including a positive electrode sheet; the positive electrode sheet is the aforementioned positive electrode sheet.

[0022] The operating voltage of the lithium-ion battery is ≥4.5 V (vs. Li+ / Li).

[0023] In the lithium-ion battery, the negative electrode material can be selected from lithium metal or graphite; the electrolyte can be selected from an organic electrolyte containing lithium salt.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention achieves a polymer that integrates three core functions—high-strength adhesion, transition metal ion migration inhibition, and interface stability regulation—through precise molecular structure design, exhibiting outstanding comprehensive performance.

[0025] The polymer provided by this invention can be used as a binder for high-voltage cathodes, exhibiting breakthrough performance advantages in high-voltage lithium-ion battery systems, including significantly improved cycle life, excellent rate performance, and superior stability. Furthermore, the polymer provided by this invention also possesses excellent electrospinning properties, allowing for the preparation of nanofiber membranes via electrospinning processes. Simultaneously, a spraying technique can be used to uniformly load active materials onto the fiber network, thereby constructing an integrated solid-state cathode material. Attached Figure Description

[0026] Figure 1 The NMR spectrum and infrared spectrum of the polymer prepared in Example 1 are shown in the figure; (a) is the NMR spectrum and (b) is the infrared spectrum.

[0027] Figure 2 A comparison of contact angle tests of electrode sheets prepared using polymers and PVDF as binders, as provided in this invention.

[0028] Figure 3 A comparison of LSV curves of electrode sheets prepared using the polymer and PVDF as binders, respectively, provided by this invention.

[0029] Figure 4 Comparison of cycle performance of high-voltage cathode lithium-ion batteries prepared using polymers and PVDF as binders, as provided in this invention.

[0030] Figure 5 Comparative calculations of the migration barriers within the Mn and Ni ion layers in high-voltage cathode lithium-ion batteries prepared using the polymer and PVDF provided in this invention as binders.

[0031] Figure 6 Micrograph of a nanofiber membrane prepared by electrospinning of a polymer provided by the present invention.

[0032] Figure 7 This image shows an integrated positive electrode formed by electrospinning nanofiber membranes coated with a binder polymer, as provided by the present invention.

[0033] Figure 8 Tensile test diagram of polymer electrospun nanofiber membrane provided by the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0036] Unless otherwise specified, all reagents, materials, instruments, etc. used in the following examples are commercially available.

[0037] The 4-cyanobutyric acid used in the following examples, CAS No. 39201-33-7, is commercially available.

[0038] Example 1: Preparation of poly(4-cyanobutyl methacrylate) (PCM) This embodiment provides a method for preparing poly(4-cyanobutyl methacrylate) (PCM), the specific steps of which are as follows: (1) Monomer synthesis Under nitrogen protection, 1 g of 4-cyanobutyric acid was dissolved in ultra-dry dichloromethane, and oxaloyl chloride was slowly added dropwise. The molar ratio of 4-cyanobutyric acid to oxaloyl chloride was 1:1.2. 15 μL of DMF was added as a catalyst. After reacting at room temperature for 5 h, the solution was purified by two dichloromethane dissolution-rotary evaporation processes to obtain a pale yellow oily 4-cyanobutyric acid chloride.

[0039] (2) The obtained 4-cyanobutyric acid chloride was dissolved in dichloromethane and then added dropwise to a dichloromethane solution containing vinyl alcohol and triethylamine under ice bath conditions. After esterification reaction for 5 h, the monomer of 4-cyanobutyric acid was purified by column chromatography.

[0040] (3) RAFT aggregation The purified 4-cyanobutyric acid vinyl ester monomer was mixed with 2,2-azobis(2-methylpropanediamine) dihydrochloride at a monomer:initiator molar ratio of 1:0.001. RAFT reagent 4-cyano-4-(thiobenzoylthio)valerate was added at an amount of 0.010% of the monomer molar. The reaction was carried out in an acetic acid buffer solution at pH 4.8-5.2 at 70°C for 5 hours, and then terminated in an ice bath to obtain the product poly(4-cyanobutyl methacrylate) (PCM).

[0041] (4) Product purification The product was purified as follows: a) washed with deionized water 3-5 times to remove acidic impurities; b) recrystallized 2-3 times with acetonitrile / water (1:1, v / v) mixed solvent; c) eluted by silica gel column chromatography gradient (dichloromethane:methanol from 20:1 to 5:1); d) freeze-dried until no monomer residue was detected by GC-MS (detection limit <0.01%).

[0042] The degree of polymerization of the polymer prepared in Example 1 was 150-300.

[0043] Example 2: Preparation of high-voltage positive electrode and lithium-ion battery Poly(4-cyanobutyl methacrylate) (PCM) prepared in Example 1 was used as a binder and mixed with conductive carbon black (Super P) and high-voltage cathode material Ni90 at a mass ratio of 1:1:8. N-methylpyrrolidone (NMP) solvent was added to form a slurry. The slurry was uniformly coated onto aluminum foil using a doctor blade, and after vacuum drying at 60°C for 12 hours, it was punched into high-voltage cathode material Ni90 with a diameter of 12 mm.

[0044] In an argon glove box, the obtained electrode sheet was used as a high-voltage positive electrode sheet, and a CR2032 button cell was assembled with a lithium metal negative electrode, a Celgard2400 separator and a high-voltage electrolyte. The cell was left to stand for 6 hours before testing.

[0045] Comparative Example The difference from Example 2 is that poly(4-cyanobutyl methacrylate) was replaced with the conventional binder PVDF to prepare the electrode sheet; and the same steps were used to further prepare the button cell.

[0046] Characterization and test results: 1. Structural characterization of polymers like Figure 1 As shown in (a), the synthesized PCM polymer was subjected to... 1 ¹H NMR characterization was performed to confirm the polymer structure. The characteristic peaks shown in the spectrum were consistent with the expected monomer structure, confirming the successful synthesis of the polymer and the integrity of the chain structure.

[0047] like Figure 1 As shown in (b), the polymer's molecular structure contains cyano groups (-CN), which form coordination bonds with transition metals in the positive electrode active material. This significantly increases the migration energy barrier of transition metal ions, forming an effective energy barrier that effectively suppresses the dissolution of transition metal ions and fundamentally alleviates the structural degradation problem of the electrode material. Furthermore, the abundant carbonyl (C=O) functional groups in the polymer preferentially adsorb lithium ions from the electrolyte due to their strong electronegativity, forming a locally high-concentration lithium-ion region at the electrode / electrolyte interface. This significantly reduces interfacial impedance and induces the formation of a uniformly distributed solid electrolyte interphase (SEI) rich in inorganic components on the nickel-rich positive electrode surface. This not only ensures interfacial stability during long-term cycling but also effectively suppresses excessive electrolyte decomposition and optimizes lithium-ion transport kinetics at the interface.

[0048] The characterization results show that the polymer backbone obtained in Example 1 has a three-dimensional network structure, which endows the material with excellent mechanical strength and adhesion properties, and can form a stable bond with the positive electrode active material, ensuring the structural integrity of the electrode under high voltage cycling conditions.

[0049] 2. Contact angle The testing method, steps, and operating conditions are as follows: Electrode sheets prepared using different binders (including the comparative PVDF binder and the PCM binder prepared in Example 1) were vacuum dried at 60°C for 12 hours before use.

[0050] The test was conducted using a contact angle meter in an environment with room temperature and relative humidity not exceeding 40%. During the test, an automatic sampler was used to drop 3 μL of electrolyte (1 mol·L⁻¹) onto the surface of the electrode. -1 LiPF6 / EC:DMC = 1:1 (volume ratio). The initial contact angle between the droplet and the electrode surface was tested using a static contact angle mode. The obtained data was automatically fitted and the average value was recorded. Five tests were performed on different regions of each sample, and the average value was taken as the final result.

[0051] The results are as follows Figure 2 As shown, compared with electrode sheets prepared by the traditional binder PVDF, the contact angle of the electrode sheets prepared by PCM is significantly reduced. This indicates that the cyano group (-CN) in the PCM molecular chain forms a strong polar interaction with the electrolyte solvent, which improves the wettability of the electrode interface and thus enhances the cycle stability.

[0052] 3. Electrochemical stability The testing method, steps, and operating conditions are as follows: Linear sweep voltammetry was used for testing. The tests were conducted under isothermal conditions using an electrochemical workstation (CHI660E, Shanghai Chenhua Co., Ltd.). The test battery was assembled using a stainless steel / PVDF membrane and a PCM membrane / lithium sheet structure. The electrolyte was 1 mol·L⁻¹. -1 LiPF6 / EC:DMC = 1:1 (volume ratio). Thin film samples were prepared using different binders. The linear scan voltage range was set to 2.0–6.0 V (vs. Li / Li). + The scan rate was 1.0 mV·s. -1 Before testing, the assembled battery was allowed to stand at room temperature for 12 hours. All electrochemical data were automatically recorded and analyzed by software.

[0053] The results are as follows Figure 3 As shown, the electrochemical window of the electrode sheet prepared by PCM can reach 5.3V, indicating that it has excellent electrochemical stability and can be matched with high-voltage cathodes.

[0054] 4. Specific capacity and cycle performance The testing method, steps, and operating conditions are as follows: Button cells (CR2032 type) were used for assembly and testing. The positive electrode was prepared by mixing and dispersing active materials (such as NCM90), conductive agents (Super P), and binders (PVDF, PCM) in DMF at a mass ratio of 8:1:1 to form a slurry. This slurry was uniformly coated onto an aluminum foil current collector, vacuum dried at 80℃ for 12 h, and then pressed and sliced ​​for later use. The negative electrode used a lithium metal sheet, the separator was polypropylene (Celgard 2400), and the electrolyte was 1 mol·L⁻¹. -1 LiPF6 / EC:DMC = 1:1 (volume ratio). Assembly was conducted in an argon-filled glove box (H2O and O2 content <0.1 ppm). Battery charge / discharge performance was tested using a Xinwei battery testing cabinet. The test voltage range was 2.8-4.3 V, the constant current charge / discharge rate was set to 1C, and cycle tests were performed at 25℃. Discharge specific capacity and capacity retention were recorded.

[0055] The results are as follows Figure 4 As shown, PCM, as a binder, can improve the performance of lithium-ion batteries through the synergistic effect of bifunctional groups, making their specific capacity and cycle performance more excellent.

[0056] 5. Calculation of ion migration barrier The calculation method is as follows: Density functional theory (DFT) calculations were performed using the Vienna Ab initio Simulation Package (VASP) to calculate the energy barriers for Mn and Ni ion migration. The calculations began with cell parameter and geometry optimization. The spin-polarized DFT+U method was employed, with U values ​​of 6.20 eV, 3.32 eV, and 3.90 eV for Ni, Co, and Mn, respectively, to accurately describe the electronic properties of the Coulomb and exchange interactions of the strongly localized Ni, Co, and Mn 3d orbitals. A 15 Å vacuum layer was added along the c-axis to avoid interactions between adjacent units. The migration barriers for Mn and Ni ions were calculated using the ramp-like elastic band method. Spin polarization was considered in all the above calculations.

[0057] The results are as follows Figure 5 As shown, in PCM-based high-voltage cathode lithium-ion batteries, nitrile groups form stable coordination bonds with surface transition metal ions, effectively anchoring them and hindering their migration paths. For the migration of Mn and Ni ions, the calculated energy barriers increase significantly from the PVDF-based model to the PCM-based model, highlighting the strong inhibitory effect of surface chelation. This confirms that coordination bonding with -CN groups effectively stabilizes the transition metal ions at their lattice positions and suppresses harmful cation mixing.

[0058] Example 3 This embodiment provides a cathode material, the preparation method of which is as follows: The polymer obtained in Example 1 was used to prepare nanofiber membranes using a conventional electrospinning process. In the electrospinning process, 13.0 wt.% of PCM powder was first dissolved in DMF solvent and stirred thoroughly at room temperature to obtain a transparent electrospinning solution. Then, the precursor solution was loaded into a syringe equipped with a stainless steel needle, and the pump feed rate was set to 0.08 mL / min. -1 The electrospinning parameters were: positive voltage 14.0 kV, negative voltage -2.0 kV, and a distance of approximately 20 cm between the ejector and collector ends. The fibers were collected by a grounded roller covered with aluminum foil. After spinning, the resulting PCM fiber membrane was dried overnight under vacuum at 60°C to thoroughly remove residual solvent. Subsequently, a simultaneous spraying technique was used to uniformly load the positive electrode active material into the fiber network structure of the nanofiber membrane, alternating between horizontal and vertical directions, to obtain an integrated solid-state positive electrode material.

[0059] like Figure 6 As shown, the nanofiber membrane prepared by electrospinning is a complex three-dimensional porous network structure formed by interwoven fibers of nanometer to micrometer scale. Its fiber surface is smooth, its diameter is uniformly distributed, and it has high specific surface area and high porosity.

[0060] like Figure 7 As shown in the figure, an integrated positive electrode structure is constructed by uniformly spraying active positive electrode particles onto the surface of electrospun binder fibers. The fiber network not only serves as a mechanical support framework, improving the structural integrity and flexibility of the electrode, but its porous interconnected structure also provides continuous channels for electrolyte wetting and ion transport. The tight coating of particles and fibers ensures good interfacial contact, reduces particle shedding and interfacial impedance, and significantly enhances the overall mechanical stability and electrochemical performance of the electrode.

[0061] like Figure 8 As shown, the nanofiber membrane prepared by electrospinning has good elasticity and toughness, and the stress-strain curve is nonlinear. It can withstand tensile force under large strain and eventually break, demonstrating mechanical properties that combine strength and flexibility.

[0062] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A polymer for use as a high-voltage positive electrode, having the general structural formula shown in Formula I: In Formula I, n ranges from 150 to 300; the degree of polymerization ranges from 150 to 300.

2. The method for preparing the polymer according to claim 1, characterized in that, Includes the following steps: S1, 4-cyanobutyric acid reacts with oxalyl chloride to form 4-cyanobutyric acid chloride; S2. The obtained 4-cyanobutyric acid chloride undergoes an esterification reaction with vinyl alcohol to obtain 4-cyanobutyric acid vinyl ester monomer; S3. The obtained 4-cyanobutyric acid vinyl ester monomer undergoes RAFT polymerization to obtain the target product.

3. The preparation method according to claim 2, characterized in that, In step S1, the molar ratio of 4-cyanobutyric acid to oxaloyl chloride is 1:(1.1-2.0). The catalyst used in the acyl chloride reaction is N,N-dimethylformamide; The conditions for the acyl chloride reaction are: temperature 20-30℃, time 5-6h.

4. The preparation method according to claim 2, characterized in that, In step S2, the molar ratio of 4-cyanobutyric acid to vinyl alcohol is 1:(1-1.2). The catalyst used in the esterification reaction is triethylamine; The conditions for the esterification reaction are: temperature 0-10℃ and time 5-6h.

5. The preparation method according to claim 2, characterized in that, In step S3, the initiator used in the RAFT polymerization reaction is 2,2-azobis(2-methylpropanediamine) dihydrochloride, and its amount is 0.01-0.1% of the molar amount of the 4-cyanobutyrate monomer; The RAFT reagent used in the RAFT polymerization reaction is 4-cyano-4-(thiobenzoylthio)pentanoic acid, and its amount is 0.005-0.05% of the molar amount of the 4-cyanobutyrate vinyl ester monomer; The conditions for RAFT polymerization are: pH of the reaction system is 4.0-6.0, temperature is 60-80℃, and time is 5-6h.

6. The preparation method according to any one of claims 1-5, characterized in that, Step S3 also includes the purification of the reaction product; The purification process includes: washing the reaction product with water 3-5 times to remove acidic impurities, recrystallizing it 2-3 times with an acetonitrile / water mixed solvent, and then eluting it using silica gel column chromatography gradient. The volume ratio of acetonitrile to water in the mixed solvent is 1:(0.5-2). The eluent in the gradient elution of the silica gel column chromatography is composed of dichloromethane and methanol; the volume ratio gradient of dichloromethane to methanol varies in the range of (3-15):

1.

7. A positive electrode material, characterized in that, It comprises the following components: a positive electrode active material, a conductive agent, and a binder; the binder is the polymer described in claim 1.

8. A positive electrode material, characterized in that, It includes a nanofiber membrane and a positive electrode active material loaded thereon; the nanofiber membrane is prepared by electrospinning of the polymer described in claim 1.

9. A positive electrode sheet, characterized in that, It is prepared using the cathode material as described in claim 7 or 8.

10. A lithium-ion battery, characterized in that, Includes a positive electrode sheet; the positive electrode sheet is the positive electrode sheet as described in claim 9.

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