Negative current collector and preparation method and application thereof

Abstract

The invention discloses a negative electrode current collector and a preparation method and application thereof, the negative electrode current collector comprises a substrate and a polyvinylidene fluoride coating coated on the surface of the substrate, and the content of beta phase in the polyvinylidene fluoride coating is greater than or equal to 80%. According to the polyvinylidene fluoride coating with high beta-phase content, a continuous and rapid Li < + > transmission channel is formed by directional C-F arrangement in a coating film, so that high ionic conductivity and uniform Li < + > flux are realized. Meanwhile, the beta-polyvinylidene fluoride with high dielectric constant promotes dissociation of lithium salt, increases the Li < + > transference number, and more free Li < + > participates in transmission, so that side reaction between an electrode and electrolyte is inhibited, and uniform and rapid charge transfer is promoted in the discharge process. In addition, coordination between Li < + > and TFSI <-> is reduced through beta-polyvinylidene fluoride, dissociation of lithium salt is promoted, a continuous and rapid Li < + > transmission channel is provided, and the electrochemical performance of the battery is further optimized.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and in particular to a negative electrode current collector, its preparation method, and its application. Background Technology

[0002] In today's rapidly developing technological era, lithium batteries, with their numerous advantages such as long cycle life, have been widely used in various portable electronic devices, electric vehicles, and large-scale energy storage systems. Energy density, a key performance indicator of lithium batteries, directly determines their applicability and competitiveness in different application scenarios. As various electrical devices increasingly demand longer battery life and extended operating time, the demand for lithium battery energy density is also growing. However, the energy density of existing lithium batteries is often insufficient to meet practical needs.

[0003] From the perspective of negative electrode structure, traditional negative electrode current collectors and their related designs have, to some extent, limited the further improvement of lithium battery energy density. On the one hand, the interface performance between traditional negative electrode current collectors and negative electrode active materials is not ideal, resulting in the active materials not being able to fully exert their energy storage function during charge and discharge, affecting the overall energy conversion efficiency and energy density of the battery. For example, problems such as high contact resistance at the interface and weak adhesion of active materials to the current collector surface prevent some active materials from effectively participating in electrochemical reactions during charge and discharge cycles, thus causing energy loss. On the other hand, the structural and performance limitations of traditional negative electrode current collectors prevent them from providing effective solutions to factors affecting battery performance and safety, such as suppressing lithium dendrite growth. The formation of lithium dendrites not only brings safety hazards, such as short circuit risks, but also occupies the effective space inside the battery, reducing the amount of active material that can be filled, thereby reducing the battery's energy density. Summary of the Invention

[0004] In order to overcome the defects in the prior art, the first objective of this invention is to provide a negative electrode current collector, the second objective of this invention is to provide a method for preparing a negative electrode current collector, the third objective of this invention is to provide a negative electrode, the fourth objective of this invention is to provide a lithium battery, and the fifth objective of this invention is to provide an electrical device.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, a negative electrode current collector includes a substrate and a polyvinylidene fluoride coating applied to the surface of the substrate, wherein the β-phase content of the polyvinylidene fluoride coating is ≥80%. Preferably, the β-phase content is ≥90%. The substrate may be copper foil.

[0007] The substrate can be copper foil, and the thickness of the copper foil is preferably 4.0μm-12.0μm, such as 4.0μm, 6.0μm, 8.0μm, 10.0μm, 12.0μm, or any value between 4.0μm and 12.0μm. Copper foil, as a current collector substrate, has high conductivity, excellent mechanical strength, and chemical stability, and can form a tight interface bond with the polyvinylidene fluoride coating, preventing coating peeling.

[0008] By controlling the β-phase content in the polyvinylidene fluoride (PVDF) coating to ≥80%, its molecular chains exhibit an all-trans zigzag planar configuration, forming a highly ordered CF polar bond arrangement, thereby constructing continuous and rapid lithium-ion transport channels within the coating. This directional arrangement significantly improves the ionic conductivity of the coating and promotes the effective dissociation of lithium salts in the electrolyte, increasing the lithium-ion transference number, reducing the coordination effect between lithium ions and anions, and suppressing side reactions at the electrode / electrolyte interface. Simultaneously, the high β-phase content coating possesses excellent dielectric properties, enhancing the compatibility between the electrode material and the electrolyte, ensuring uniform and efficient lithium-ion insertion / extraction during charging and discharging. Ultimately, this improves the specific capacity of the cell at 0.5C rate, and significantly enhances cycle stability compared to traditional low-β-phase or uncoated current collectors. Furthermore, this technology eliminates the need for complex processes or expensive additives, directly increasing energy density within standard cell size and effectively reducing cost per watt-hour.

[0009] Preferably, the thickness of the polyvinylidene fluoride (PVDF) coating is 0.1-1 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, or any value between 0.1 and 1.0 μm. By controlling the thickness of the PVDF coating within the range of 0.1 μm to 1 μm, the uniformity of the coating, lithium-ion transport efficiency, and interface stability can be balanced. When the coating thickness is less than 0.1 μm, it may lead to discontinuities or pinhole defects in the coating, affecting electrolyte wettability and triggering local side reactions; while when the thickness exceeds 1 μm, the internal impedance of the coating increases significantly, hindering the rapid migration of lithium ions, and may also lead to a decrease in the adhesion between the coating and the substrate. A preferred thickness range of 0.1µm to 1µm ensures that the coating forms a dense and continuous thin film structure at the microscale. The internal β-phase polyvinylidene fluoride molecular chains (all-trans planar zigzag configuration) fully expose the polar CF bonds, enhancing the dissociation ability of lithium salts in the electrolyte and constructing lithium-ion transport channels throughout the coating. Furthermore, this thickness range is highly compatible with spin-coating process parameters, ensuring coating uniformity while avoiding material waste. This allows for increased energy density within a limited cell size and avoids increasing battery internal resistance or affecting the feasibility of electrode rolling processes due to excessive coating thickness.

[0010] Secondly, a method for preparing the above-mentioned negative electrode current collector includes the following steps:

[0011] Polyvinylidene fluoride was dissolved in N,N-dimethylacetamide to form a premixed polyvinylidene fluoride solution;

[0012] The premixed polyvinylidene fluoride solution was stirred and ultrasonically treated to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0013] A polyvinylidene fluoride solution is coated onto the substrate surface to form a coating film.

[0014] A substrate with a coated film is placed on a heating device under inert gas protection to evaporate the solvent, thereby obtaining a negative electrode current collector covered with a polyvinylidene fluoride coating, wherein the β phase content of the polyvinylidene fluoride coating is ≥80%.

[0015] Optionally, the solvent evaporation temperature is 40-85℃, such as any value between 40℃, 50℃, 60℃, 70℃, 80℃, 85℃ or 40-85℃.

[0016] By controlling the solvent evaporation temperature within the range of 40-85℃, the polyvinylidene fluoride (PVDF) molecular chains are induced to transform from the nonpolar α phase to the polar β phase (orthorhombic crystal system, all-inverse planar serrated configuration). This low-temperature evaporation process is carried out under inert gas protection, which prevents copper foil oxidation and PVDF thermal decomposition, ensuring the stability of the coating structure with a β phase content ≥80%. In the PVDF coating with high β phase content, the oriented CF polar bonds form continuous lithium-ion transport channels, improving ionic conductivity and lithium-ion transference number, and significantly suppressing lithium dendrite growth and electrode / electrolyte interface side reactions. Furthermore, this process does not require high-temperature treatment or complex equipment, is compatible with existing lithium battery manufacturing processes, and reduces mass production costs.

[0017] Optionally, the inert gas may be argon.

[0018] Optionally, the evaporation time is 90-95 minutes.

[0019] By controlling the solvent evaporation temperature within the range of 40°C to 85°C, such as 40°C, 60°C, 80°C, or 85°C, and combining this with an evaporation time of 90-95 minutes, the slow volatilization of N,N-dimethylacetamide (DMAc) can be achieved under inert gas protection. This allows for the regulation of the directional alignment of polyvinylidene fluoride (PVDF) molecular chains from the disordered α-phase (hexagonal crystal system) to the highly polar β-phase (orthorhombic crystal system, all-inverse planar serrated configuration). Below 40°C, the solvent evaporation rate is too slow, leading to low process efficiency; while above 85°C, rapid solvent evaporation disrupts the molecular chain order, significantly reducing the β-phase content. The 90-95 minute evaporation time ensures thorough solvent removal while avoiding copper foil oxidation or PVDF thermal decomposition caused by prolonged high-temperature heating.

[0020] Preferably, the stirring is performed using magnetic stirring for 12-14 hours, such as 12, 13, or 14 hours, or any value between 12 and 14 hours. By continuously stirring the mixed solution of polyvinylidene fluoride (PVDF) and N,N-dimethylacetamide (DMAc) for 12-14 hours using magnetic stirring, the PVDF molecular chains can be fully untangled and uniformly dispersed in the solvent, avoiding local agglomeration or the presence of undissolved particles. When the stirring time is less than 12 hours, the solution homogeneity is insufficient, and the coating after spin-coating is prone to microcracks or uneven thickness, leading to a decrease in ionic conductivity. However, stirring times exceeding 14 hours may cause solvent evaporation or thermal effects, affecting the stability of the solution.

[0021] Optionally, the polyvinylidene fluoride (PVDF) solution is coated onto the substrate surface using a spin-coating process at a speed of 2000-4000 rpm for 10-12 seconds. Spin-coating is a coating technique that uses centrifugal force to uniformly spread the solution into a film by rotating the substrate at high speed. Spin-coating the PVDF solution onto the copper foil substrate surface at a speed of 2000-4000 rpm for 10-12 seconds yields a coating with uniform thickness and good density, ensuring a smooth and defect-free coating surface. When the speed is below 2000 rpm or the time is less than 10 seconds, insufficient centrifugal force may lead to uneven solution spreading, forming areas that are too thick or too thin, causing the lithium-ion transport path to break and the interfacial impedance to increase. When the speed exceeds 4000 rpm or the time exceeds 12 seconds, the solvent evaporates prematurely, which may cause microcracks in the coating and reduce the β-phase content.

[0022] Preferably, the ratio of polyvinylidene fluoride (PVDF) to N,N-dimethylacetamide (DMAc) is 1 g:(8-12) mL. More preferably, the ratio of PVDF to N,N-dimethylacetamide is 1 g:10 mL. Controlling the ratio of PVDF to N,N-dimethylacetamide (DMAc) within the range of 1 g:(8-12) mL, preferably 1 g:10 mL, balances the solubility and rheological properties of the solution, ensuring the stability and consistency of the coating preparation process. When the ratio is lower than 1 g:12 mL, the excessive solvent leads to excessively low solution viscosity, which easily causes sagging or uneven coating thickness during spin coating; while when the ratio is higher than 1 g:8 mL, the entanglement of PVDF molecular chains intensifies, the solution viscosity becomes too high, and it is difficult to form a uniform film through spin coating. Specifically, a 1g:10mL dosage ratio ensures that PVDF is fully dispersed into a homogeneous solution through intermolecular hydrogen bonds and dipole interactions, and the solution viscosity is highly compatible with the spin-coating process (2000-4000 rpm). At this ratio, during solvent evaporation, the PVDF molecular chains are orderly arranged under the plasticizing effect of DMAc, increasing the β-phase content. Furthermore, a dosage ratio of 1g:(8-12)mL avoids interfacial side reactions caused by excessive solvent residue or electrode rolling cracking due to excessively high PVDF concentration, ensuring that the specific capacity of the cell remains stable at 143-145mAh / g at 0.5C rate, with a capacity retention of >90% after 500 cycles.

[0023] Thirdly, a negative electrode includes the aforementioned negative electrode current collector and a negative electrode active material coated on the surface of the negative electrode current collector.

[0024] The negative electrode active material is selected from at least one of graphite, silicon-based materials, hard carbon, or soft carbon. The silicon-based material may be a silicon-carbon composite material or a silicon-oxygen negative electrode. Preferably, the negative electrode active material is composed of the following components in weight percentage:

[0025] The graphite content is 94% to 98%, more preferably 96.4%;

[0026] The binder content is 1.5% to 3%, more preferably 2.3%, and the binder is LA136D;

[0027] The conductive agent content is 0.5% to 1.5%, more preferably 0.9%, and the conductive agent is Super P;

[0028] The content of the thickener is 0.3% to 0.6%, more preferably 0.4%, and the thickener is sodium carboxymethyl cellulose (CMC).

[0029] Fourthly, a lithium battery comprising the aforementioned negative electrode.

[0030] Optionally, the lithium battery includes the aforementioned negative electrode, positive electrode, electrolyte, and separator, wherein the active material of the positive electrode is at least one of lithium iron phosphate, ternary materials (such as lithium nickel cobalt manganese oxide), or lithium cobalt oxide, preferably composed of lithium iron phosphate, conductive agent Super P, binder PVDF5130, and carbon nanotubes in a weight ratio of 96:1.8:1.7:0.5, and the positive electrode active surface density is 16.0 mg / cm³. 2 The electrolyte contains 1M lithium hexafluorophosphate (LiPF6) and a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. The separator is a ceramic-coated polyethylene film.

[0031] Fifthly, an electrical device includes the aforementioned lithium battery.

[0032] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0033] 1. The β-phase content of the polyvinylidene fluoride (PVDF) coating on the surface of the negative electrode current collector is ≥80%. The β-phase crystal structure of PVDF is regular and highly polar, enabling it to form various strong interactions with the negative electrode active material (such as van der Waals forces and dipole-dipole interactions), adhering to the active material like a "molecular glue." Simultaneously, the high β-phase content of the PVDF coating results in excellent mechanical properties, buffering the stress caused by volume changes in the active material during charge and discharge. Furthermore, its good chemical stability allows it to maintain interfacial stability in complex chemical environments. These factors combined result in a tighter interfacial bond between the negative electrode current collector and the negative electrode active material, effectively reducing the shedding of the negative electrode active material during charge-discharge cycles, thereby improving the battery's cycle stability and capacity retention.

[0034] 2. The regular crystal structure and suitable surface energy of the β-phase PVDF coating can alter the deposition behavior of lithium, making lithium more prone to uniform nucleation and growth during deposition, rather than forming sharp lithium dendrites. Simultaneously, the tight bonding between the coating and the negative electrode active material, as well as its own stability, helps maintain the uniformity of the electric field distribution inside the battery, further suppressing the formation of lithium dendrites. This reduces safety risks such as short circuits caused by lithium dendrites, prevents lithium dendrites from occupying the internal space of the battery, helps maintain the stability of the internal battery structure, and thus improves the overall performance of the battery.

[0035] 3. Polyvinylidene fluoride coatings with high β-phase content exhibit continuous and rapid Li-phase formation due to the oriented CF arrangement within the coating film. + The transport channel achieves high ionic conductivity and uniform Li + Flux. Simultaneously, the high dielectric constant of β-polyvinylidene fluoride promotes the dissociation of lithium salts, increasing Li... + Migration numbers, more freedom Li +Participating in charge transport helps suppress side reactions between the electrode and electrolyte and promotes uniform and rapid charge transfer during discharge. Furthermore, β-polyvinylidene fluoride reduces Li... + With TFSI - The coordination between them promotes the dissociation of lithium salt and provides continuous and rapid Li-24O3 dissociation. + The transmission channel further optimizes the electrochemical performance of the battery.

[0036] 4. During the preparation of the negative electrode current collector, key parameters of each process step were precisely controlled. For example, the ratio of polyvinylidene fluoride (PVDF) to N,N-dimethylacetamide was 1 g:(8-12) mL. This ratio ensures that PVDF is fully dissolved in the solvent and forms a solution of suitable concentration, which is beneficial for the formation and performance of the subsequent coating. Magnetic stirring for 12-14 hours combined with ultrasonic treatment effectively removes air bubbles, making the solution uniform and defect-free. The spin coating process uses a rotation speed of 2000-4000 rpm and a time of 10-12 seconds to ensure uniform coating thickness. The solvent evaporation temperature is between 40℃ and 85℃ (preferably 40℃ to 80℃) and the evaporation time is 90-95 minutes. The precise control of these parameters ensures the stability and consistency of the quality and performance of the PVDF coating.

[0037] 5. The entire preparation process is relatively mature and stable. Operations such as magnetic stirring, spin coating, and solvent evaporation under inert gas protection are all carried out under conventional and controllable conditions. The equipment and technologies involved in these operations are already mature in industrial production, easy to control precisely and for large-scale stable production, which can effectively ensure the stability and consistency of product quality.

[0038] 6. Due to the advantages of the aforementioned negative electrode current collector in terms of interfacial bonding, suppression of lithium dendrite growth, and optimization of ionic conductivity, lithium batteries prepared using the negative electrode current collector of this invention exhibit significantly improved key performance indicators such as cycle performance, safety, and ion transport performance. In the field of electric vehicles, better cycle stability can improve driving range, enhanced safety helps extend battery life, and good ionic conductivity helps improve battery charge and discharge performance. In the field of portable electronic devices, stable performance can enhance safety and stability, thereby better meeting the needs of various electrical devices for high-performance lithium batteries.

[0039] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 These are the XRD patterns from Embodiments 1-3 and Comparative Examples 1-3 of the present invention;

[0042] Figure 2 These are the infrared spectra from Embodiments 1-3 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] An embodiment of the present invention provides a negative electrode current collector, comprising a substrate and a polyvinylidene fluoride coating coated on the surface of the substrate, wherein the β phase content of the polyvinylidene fluoride coating is ≥80%.

[0045] In some alternative embodiments, the thickness of the polyvinylidene fluoride coating is from 0.1 μm to 1 μm, such as any value between 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm or 0.1-1 μm.

[0046] The embodiments of the present invention also provide a method for preparing the above-mentioned negative electrode current collector, comprising the following steps:

[0047] Polyvinylidene fluoride was dissolved in N,N-dimethylacetamide to form a premixed polyvinylidene fluoride solution;

[0048] The premixed polyvinylidene fluoride solution was stirred and ultrasonically treated to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0049] A polyvinylidene fluoride solution is coated onto the substrate surface to form a coating film.

[0050] A substrate with a coated film is placed on a heating device under inert gas protection to evaporate the solvent, thereby obtaining a negative electrode current collector covered with a polyvinylidene fluoride coating, wherein the β phase content of the polyvinylidene fluoride coating is ≥80%.

[0051] In some alternative embodiments, the solvent evaporation temperature is between 40°C and 85°C, such as any value between 40°C, 50°C, 60°C, 70°C, 80°C, 85°C, or 40-85°C. The evaporation time is 90-95 minutes, such as any value between 90 minutes, 91 minutes, 92 minutes, 93 minutes, 94 minutes, 95 minutes, or 90-95 minutes.

[0052] In some alternative embodiments, the stirring is performed using magnetic stirring for a duration of 12-14 hours, such as 12 hours, 13 hours, 14 hours, or any value between 12 and 14 hours.

[0053] In some optional embodiments, the polyvinylidene fluoride solution is coated onto the substrate surface via spin coating at a rotation speed of 2000-4000 rpm, such as any value between 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, or 2000-4000 rpm. The spin coating time is 10-12 seconds, such as any value between 10 seconds, 11 seconds, 12 seconds, or 10-12 seconds.

[0054] In some optional embodiments, the ratio of polyvinylidene fluoride to N,N-dimethylacetamide is 1 g:(8-12) mL. Preferably, the ratio of polyvinylidene fluoride to N,N-dimethylacetamide is 1 g:10 mL.

[0055] The embodiments of the present invention also provide a negative electrode, including the above-mentioned negative electrode current collector and a negative electrode active material coated on the surface of the negative electrode current collector.

[0056] The embodiments of the present invention also provide a lithium battery, including the above-described negative electrode.

[0057] The embodiments of the present invention also provide an electrical device including the above-described lithium battery.

[0058] Example 1:

[0059] This embodiment provides a method for preparing a negative electrode current collector, including the following steps:

[0060] Weigh 1g of commercially available polyvinylidene fluoride and dissolve it in 10mL of commercially available N,N-dimethylacetamide. Stir the solution magnetically for 12h at room temperature and then sonicate it for 30min to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0061] A 6.0 μm thick smooth copper foil was used as the spin-coating substrate, pre-cleaned with dilute hydrochloric acid and dried. Polyvinylidene fluoride solution was dropped onto the copper foil surface and spread out, then spin-coated at 3000 rpm for 10 seconds to form a uniform PVDF film.

[0062] A copper foil coated with a PVDF film was placed on a heating plate under argon protection and heated at 40°C for 90 minutes to allow N,N-dimethylacetamide to slowly evaporate, thus preparing the negative electrode current collector. The resulting coating was labeled PVDF40@Cu, where 40 represents the evaporation temperature in °C.

[0063] This embodiment also provides a method for preparing a negative electrode, including the following steps:

[0064] Graphite, binder LA136D, conductive agent Super P and thickener CMC were mixed in a weight ratio of 96.4:2.3:0.9:0.4, deionized water was added and stirred until a uniform negative electrode slurry was formed.

[0065] Using the negative electrode current collector prepared above as a substrate, the negative electrode slurry was mixed at 10.1 mg / cm³. 2 The areal density is uniformly coated on the surface of the PVDF40@Cu coating, and after vacuum drying at 80℃ for 12 hours and roll pressing, a complete negative electrode sheet is obtained.

[0066] Example 2:

[0067] This embodiment provides a method for preparing a negative electrode current collector, including the following steps:

[0068] Weigh 1g of commercially available polyvinylidene fluoride and dissolve it in 10mL of commercially available N,N-dimethylacetamide. Stir the solution magnetically for 12h at room temperature and then sonicate it for 30min to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0069] A 6.0 μm thick smooth copper foil was used as the spin-coating substrate, pre-cleaned with dilute hydrochloric acid and dried. Polyvinylidene fluoride solution was dropped onto the copper foil surface and spread out, then spin-coated at 3000 rpm for 10 seconds to form a uniform PVDF film.

[0070] A copper foil coated with a PVDF film was placed on a heating plate under argon protection and heated at 60°C for 90 minutes to allow N,N-dimethylacetamide to slowly evaporate, thus preparing the negative electrode current collector. The resulting coating was labeled PVDF60@Cu, where 60 represents the evaporation temperature in °C.

[0071] This embodiment also provides a method for preparing a negative electrode, including the following steps:

[0072] Graphite, binder LA136D, conductive agent Super P and thickener CMC were mixed in a weight ratio of 96.4:2.3:0.9:0.4, deionized water was added and stirred until a uniform negative electrode slurry was formed.

[0073] Using the negative electrode current collector prepared above as a substrate, the negative electrode slurry was mixed at 10.1 mg / cm³. 2 The areal density is uniformly coated on the surface of the PVDF60@Cu coating, and after vacuum drying at 80℃ for 12 hours and roll pressing, a complete negative electrode sheet is obtained.

[0074] Example 3:

[0075] This embodiment provides a method for preparing a negative electrode current collector, including the following steps:

[0076] Weigh 1g of commercially available polyvinylidene fluoride and dissolve it in 10mL of commercially available N,N-dimethylacetamide. Stir the solution magnetically for 12h at room temperature and then sonicate it for 30min to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0077] A 6.0 μm thick smooth copper foil was used as the spin-coating substrate, pre-cleaned with dilute hydrochloric acid and dried. Polyvinylidene fluoride solution was dropped onto the copper foil surface and spread out, then spin-coated at 3000 rpm for 10 seconds to form a uniform PVDF film.

[0078] A copper foil coated with a PVDF film was placed on a heating plate under argon protection and heated at 80°C for 90 minutes to allow N,N-dimethylacetamide to slowly evaporate, thus preparing the negative electrode current collector. The resulting coating was labeled PVDF80@Cu, where 80 represents the evaporation temperature in °C.

[0079] This embodiment also provides a method for preparing a negative electrode, including the following steps:

[0080] Graphite, binder LA136D, conductive agent Super P and thickener CMC were mixed in a weight ratio of 96.4:2.3:0.9:0.4, deionized water was added and stirred until a uniform negative electrode slurry was formed.

[0081] Using the negative electrode current collector prepared above as a substrate, the negative electrode slurry was mixed at 10.1 mg / cm³. 2 The areal density is uniformly coated on the surface of the PVDF80@Cu coating, and after vacuum drying at 80℃ for 12 hours and roll pressing, a complete negative electrode sheet is obtained.

[0082] Comparative Example 1:

[0083] This comparative example provides a method for preparing a negative electrode current collector, including the following steps:

[0084] Weigh 1g of commercially available polyvinylidene fluoride and dissolve it in 10mL of commercially available N,N-dimethylacetamide. Stir the solution magnetically for 12h at room temperature and then sonicate it for 30min to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0085] A 6.0 μm thick smooth copper foil was used as the spin-coating substrate, pre-cleaned with dilute hydrochloric acid and dried. Polyvinylidene fluoride solution was dropped onto the copper foil surface and spread out, then spin-coated at 3000 rpm for 10 seconds to form a uniform PVDF film.

[0086] A copper foil coated with a PVDF film was placed on a heating plate under argon protection and heated at 100°C for 90 minutes to allow N,N-dimethylacetamide to slowly evaporate, thus preparing the negative electrode current collector. The resulting coating was labeled PVDF100@Cu, where 100 represents the evaporation temperature in °C.

[0087] This comparative example also provides a method for preparing a negative electrode, including the following steps:

[0088] Graphite, binder LA136D, conductive agent Super P and thickener CMC were mixed in a weight ratio of 96.4:2.3:0.9:0.4, deionized water was added and stirred until a uniform negative electrode slurry was formed.

[0089] Using the negative electrode current collector prepared above as a substrate, the negative electrode slurry was mixed at 10.1 mg / cm³. 2 The areal density is uniformly coated on the surface of PVDF100@Cu coating, and after vacuum drying at 80℃ for 12 hours and roll pressing, a complete negative electrode sheet is obtained.

[0090] Comparative Example 2:

[0091] This comparative example provides a method for preparing a negative electrode current collector, including the following steps:

[0092] Weigh 1g of commercially available polyvinylidene fluoride and dissolve it in 10mL of commercially available N,N-dimethylacetamide. Stir the solution magnetically for 12h at room temperature and then sonicate it for 30min to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0093] A 6.0 μm thick smooth copper foil was used as the spin-coating substrate, pre-cleaned with dilute hydrochloric acid and dried. Polyvinylidene fluoride solution was dropped onto the copper foil surface and spread out, then spin-coated at 3000 rpm for 10 seconds to form a uniform PVDF film.

[0094] A copper foil coated with a PVDF film was placed on a heating plate under argon protection and heated at 120°C for 90 minutes to allow N,N-dimethylacetamide to slowly evaporate, thus preparing the negative electrode current collector. The resulting coating was labeled PVDF120@Cu, where 120 represents the evaporation temperature in °C.

[0095] This comparative example also provides a method for preparing a negative electrode, including the following steps:

[0096] Graphite, binder LA136D, conductive agent Super P and thickener CMC were mixed in a weight ratio of 96.4:2.3:0.9:0.4, deionized water was added and stirred until a uniform negative electrode slurry was formed.

[0097] Using the negative electrode current collector prepared above as a substrate, the negative electrode slurry was mixed at 10.1 mg / cm³. 2 The areal density is uniformly coated on the surface of PVDF120@Cu coating, and after vacuum drying at 80℃ for 12 hours and roll pressing, a complete negative electrode sheet is obtained.

[0098] Comparative Example 3:

[0099] This comparative example provides a method for preparing a negative electrode current collector, including the following steps:

[0100] Weigh 1g of commercially available polyvinylidene fluoride and dissolve it in 10mL of commercially available N,N-dimethylacetamide. Stir the solution magnetically for 12h at room temperature and then sonicate it for 30min to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0101] A 6.0 μm thick smooth copper foil was used as the spin-coating substrate, pre-cleaned with dilute hydrochloric acid and dried. Polyvinylidene fluoride solution was dropped onto the copper foil surface and spread out, then spin-coated at 3000 rpm for 10 seconds to form a uniform PVDF film.

[0102] A copper foil coated with a PVDF film was placed on a heating plate under argon protection and heated at 140°C for 90 minutes to allow N,N-dimethylacetamide to slowly evaporate, thus preparing the negative electrode current collector. The resulting coating was labeled PVDF140@Cu, where 140 represents the evaporation temperature in °C.

[0103] This comparative example also provides a method for preparing a negative electrode, including the following steps:

[0104] Graphite, binder LA136D, conductive agent Super P and thickener CMC were mixed in a weight ratio of 96.4:2.3:0.9:0.4, deionized water was added and stirred until a uniform negative electrode slurry was formed.

[0105] Using the negative electrode current collector prepared above as a substrate, the negative electrode slurry was mixed at 10.1 mg / cm³. 2 The areal density is uniformly coated on the surface of PVDF140@Cu coating, and after vacuum drying at 80℃ for 12 hours and roll pressing, a complete negative electrode sheet is obtained.

[0106] Comparative Example 4:

[0107] This comparative example provides a method for preparing a negative electrode current collector, including the following steps:

[0108] Weigh 1g of commercially available polyvinylidene fluoride and dissolve it in 10mL of commercially available N,N-dimethylacetamide. Stir the solution magnetically for 12h at room temperature and then sonicate it for 30min to remove air bubbles, thus obtaining a polyvinylidene fluoride solution.

[0109] A 6.0 μm thick smooth copper foil was used as the spin-coating substrate, which was pre-cleaned with dilute hydrochloric acid and dried. Polyvinylidene fluoride solution was dropped onto the surface of the copper foil and spread out. The foil was then spin-coated at 3000 rpm for 10 seconds to form a uniform PVDF film, thus preparing the negative electrode current collector.

[0110] This comparative example also provides a method for preparing a negative electrode, including the following steps:

[0111] Graphite, binder LA136D, conductive agent Super P and thickener CMC were mixed in a weight ratio of 96.4:2.3:0.9:0.4, deionized water was added and stirred until a uniform negative electrode slurry was formed.

[0112] Using the negative electrode current collector prepared above as a substrate, the negative electrode slurry was mixed at 10.1 mg / cm³. 2 The areal density is uniformly coated on the PVDF coating surface, and after vacuum drying at 80℃ for 12 hours and roll pressing, a complete negative electrode sheet is obtained.

[0113] Comparative Example 5:

[0114] In this comparative example, copper foil is used as the negative electrode current collector.

[0115] Graphite, binder LA136D, conductive agent Super P and thickener CMC were mixed in a weight ratio of 96.4:2.3:0.9:0.4, deionized water was added and stirred until a uniform negative electrode slurry was formed.

[0116] Using copper foil as a substrate, the negative electrode paste was prepared at a concentration of 10.1 mg / cm³. 2 The areal density is uniformly coated on the surface of copper foil, and after vacuum drying at 80℃ for 12 hours and roll pressing, a complete negative electrode sheet is obtained.

[0117] Lithium-ion batteries were prepared using the negative electrode sheets from Examples 1-3 and Comparative Examples 1-5 described above. The composition of these lithium-ion batteries includes:

[0118] The positive electrode was prepared using lithium iron phosphate (LiFePO4) as the active material, which was mixed with conductive carbon black, polyvinylidene fluoride, and carbon nanotubes in a mass ratio of 96:1.8:1.7:0.5 to form a slurry. The coating amount of active material on each side of the positive electrode was 16.0 mg / cm².2 It is evenly coated on the surface of the aluminum foil current collector.

[0119] The negative electrode is the same as the negative electrode used in Examples 1-3 and Comparative Examples 1-5.

[0120] The electrolyte consists of lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol / L as the lithium salt, and ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 as the solvent.

[0121] The diaphragm is made of ceramic-coated polyethylene film.

[0122] The capacity ratio (N / P ratio) of the negative electrode to the positive electrode is 1.13, and the charge / discharge voltage range is 2.0-4.5V.

[0123] The PVDF40@Cu coating, PVDF60@Cu coating, PVDF80@Cu coating, PVDF100@Cu coating, PVDF120@Cu coating, and PVDF140@Cu coating prepared in Examples 1-3 and Comparative Examples 1-3 were tested using an X-ray diffractometer (XRD, XpertPro MPD, Cu Kα).

[0124] See Figure 1 The figures show the XRD test results of Examples 1-3 and Comparative Examples 1-3. As can be seen from the figures, the polyvinylidene fluoride coatings prepared at different evaporation temperatures exhibit significant differences in the position and intensity of diffraction peaks. The diffraction peaks at 17.66°, 18.30°, and 19.90° correspond to the (100), (020), and (110) crystal planes of the α-phase polyvinylidene fluoride, while the characteristic peak at 20.26° is an overlapping peak of the (110) and (200) crystal planes of the β-phase. As the solvent evaporation temperature decreases from 140°C to 40°C, the intensity of the α-phase characteristic peak gradually weakens until it disappears, while the β-phase peak gradually becomes dominant. Taking the PVDF40@Cu coating of Example 1 (40℃) as an example, only a strong β-phase peak was observed at 20.26° in its XRD pattern, indicating that there was almost no α-phase in the coating. In contrast, the PVDF140@Cu coating of Comparative Example 1 (140℃) still showed obvious α-phase diffraction peaks at 17.66° and 19.90°, and the intensity of the β-phase peak was significantly reduced. This phenomenon is consistent with the Fourier transform infrared spectroscopy analysis results, confirming that low-temperature evaporation (40-85℃) can effectively promote the transformation of polyvinylidene fluoride molecular chains to the β-phase (all-trans planar zigzag configuration), while high-temperature conditions (100-140℃) lead to disordered molecular chain arrangement and an increase in α-phase content. Furthermore, the XRD patterns of Examples 2 (60℃) and 3 (80℃) show that the intensity of the β-phase peak slightly decreased with increasing temperature, but still maintained a high degree of crystallinity, further verifying the regulatory effect of solvent evaporation temperature on the β-phase content.

[0125] The PVDF40@Cu, PVDF60@Cu, PVDF80@Cu, PVDF100@Cu, PVDF120@Cu, and PVDF140@Cu coatings prepared in Examples 1-3 and Comparative Examples 1-3 were analyzed for polyvinylidene fluoride β-phase content using Fourier transform infrared spectroscopy (FTIR). Specifically, PVC coatings prepared at different evaporation temperatures were tested using FTIR to obtain their infrared spectra.

[0126] See Figure 2 The image shows the infrared spectra corresponding to Examples 1-3 and Comparative Examples 1-3. All coatings showed infrared spectra at 614, 766, 840, and 877 cm⁻¹. -1 All regions show characteristic FTIR absorption bands. Among them, 614 cm⁻¹... -1 (CF2 bending vibration) and 766cm -1 (Molecular chain backbone bending vibration) is a characteristic peak of the α phase, 840 cm⁻¹ -1 (CH2 rocking vibration) is a characteristic peak of the β phase, 877 cm⁻¹. -1 The strong absorption peak at this point is attributed to the symmetric stretching vibration of the C-C bond and can be used as an internal standard peak to correct for differences in sample thickness. Looking at the peak intensity changes, as the solvent evaporation temperature increases from 40℃ to 140℃, the peak intensity at 840 cm⁻¹ in Examples 1-3 decreases. -1 The intensity of the β phase peak at 614 cm⁻¹ gradually decreases, while in Comparative Examples 1-3, the intensity at 614 cm⁻¹ decreases. -1 and 766cm -1 The intensity of the α-phase peak gradually increases at 840 cm⁻¹. For example, the PVDF40@Cu coating of Example 1 (40°C) shows an increase at 840 cm⁻¹. -1 The β phase peak is significantly strong, and the α phase peak almost disappears. In Example 3 (80℃), the intensity of the β phase peak in the PVDF80@Cu coating is slightly reduced, but it is still significantly higher than the α phase peak. In Comparative Example 3 (140℃), the intensity of the α phase peak in the PVDF140@Cu coating exceeds that of the β phase peak.

[0127] According to the Lambert-Beer law, through the formula... Using 766 and 840cm -1The β-phase content of PVDF was calculated using the characteristic absorption peaks at the specified locations. The β-phase contents of Examples 1-3 were 95%, 93%, and 86%, respectively, all meeting the technical requirement of ≥80%. However, the β-phase contents of Comparative Examples 1-3 decreased sequentially to 72%, 45%, and 11% with increasing temperature, further confirming that the solvent evaporation temperature of 40-85℃ can effectively induce the formation of a fully trans-planar zigzag β-phase crystal in polyvinylidene fluoride (PVDF) molecules. High-temperature conditions lead to disordered molecular chain arrangement, promoting the formation of the nonpolar α-phase. This result is completely consistent with the trend of decreasing β-phase diffraction peak intensity with increasing temperature observed in XRD tests, verifying the crucial role of low-temperature evaporation technology in increasing the β-phase content at the molecular structure level.

[0128] The polyvinylidene fluoride coatings in Examples 1-3 and Comparative Examples 1-3 were subjected to ionic conductivity tests using electrochemical impedance spectroscopy (EIS) and chronoamperometry. During the tests, the electrode spacing L (cm), electrode area S (cm²), and ohmic impedance Rb were first measured using EIS. The ionic conductivity was calculated using the formula: σs = L / (Rb*S).

[0129] First, use EIS to measure the electrode spacing (L) (cm) and electrode area (S) (cm²). 2 The ionic conductivity was calculated using the formula σs = L / (Rb*S) based on the interfacial impedance (R_b) and ohmic impedance (R_b). Simultaneously, a 10mV DC voltage was applied for 10,000 seconds of polarization, and the initial current (I0) and steady-state current (Is) were recorded. Combined with the interfacial impedances (R0) and (Rs) before and after polarization, the ionic conductivity was calculated using the formula... Calculate Li + Number of migrations.

[0130] Capacity performance testing: CR2032 coin cells were assembled using the LAND CT2001A battery testing system. The test subjects were negative electrodes coated with polyvinylidene fluoride (PVDF) coatings of varying β-phase content (Examples 1-3, Comparative Examples 1-4), and Comparative Example 5 (bare copper current collector). The negative electrode active material was graphite (area density 10.1 mg / cm³). 2 The cathode is lithium iron phosphate (LFP), the electrolyte is 1M LiPF6 / EC:EMC (3:7 volume ratio), and the separator is a ceramic-coated polyethylene film. During the test, it was cycled 50 times at a constant current charge-discharge rate of 0.5C (voltage window 2.0-4.5V). The discharge capacity of the 10th cycle was recorded and the specific capacity (mAh / g) was calculated.

[0131] The test results are shown in the table below:

[0132]

[0133] The test results show that the β-phase content exhibits a significant positive correlation with ionic conductivity, lithium-ion transference number, and capacity. In Examples 1-3, as the β-phase content decreased from 95% to 86%, the ionic conductivity decreased from 40 × 10⁻⁶ to 40 × 10⁻⁶. -5 S / cm decreased to 7.1×10 -5 The S / cm and lithium-ion transference number decreased from 0.652 to 0.413, but were still significantly higher than those of Comparative Examples 1-5. Specifically, Example 1 (95% β phase) showed an ionic conductivity 36 times higher than Comparative Example 5 (bare copper current collector), a lithium-ion transference number nearly 1.7 times higher, and a 0.5C capacity of 145 mAh / g, a 2.8% improvement over Comparative Example 5. This indicates that when the β phase content is ≥80%, the oriented CF polar bonds in the coating can construct efficient lithium-ion transport channels, reduce interfacial impedance, and promote lithium salt dissociation. In contrast, for Comparative Examples 1-3, as the solvent evaporation temperature increased to 100-140℃, the β phase content decreased to 72%-11%, and the ionic conductivity and transference number dropped sharply. In particular, the performance of Comparative Example 3 (11% β phase) was close to that of uncoated copper foil, confirming that an increased α phase proportion under high-temperature conditions disrupts the lithium-ion transport pathway. Furthermore, Comparative Example 4 (0% β phase) without solvent evaporation and Comparative Example 5 with pure copper foil showed the worst performance, further verifying the core role of the high β phase coating in improving electrochemical performance.

[0134] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A negative electrode current collector, characterized in that: It includes a substrate and a polyvinylidene fluoride coating applied to the surface of the substrate, wherein the β phase content of the polyvinylidene fluoride coating is ≥80%.

2. The negative electrode current collector according to claim 1, characterized in that, The thickness of the polyvinylidene fluoride coating is 0.1-1 μm.

3. A method for preparing a negative electrode current collector as described in any one of claims 1-2, characterized in that, Includes the following steps: Polyvinylidene fluoride was dissolved in N,N-dimethylacetamide to form a premixed polyvinylidene fluoride solution; The premixed polyvinylidene fluoride solution was stirred and ultrasonically treated to remove air bubbles, thus obtaining a polyvinylidene fluoride solution. A polyvinylidene fluoride solution is coated onto the substrate surface to form a coating film. A substrate with a coated film is placed on a heating device under inert gas protection to evaporate the solvent, thereby obtaining a negative electrode current collector covered with a polyvinylidene fluoride coating, wherein the β phase content of the polyvinylidene fluoride coating is ≥80%.

4. The preparation method according to claim 3, characterized in that, The solvent is evaporated at a temperature of 40-85℃ for 90-95 minutes.

5. The preparation method according to claim 3, characterized in that, The stirring is done using magnetic stirring, and the stirring time is 12-14 hours.

6. The preparation method according to claim 3, characterized in that, The polyvinylidene fluoride solution is coated onto the substrate surface by spin coating at a speed of 2000-4000 rpm for 10-12 seconds.

7. The preparation method according to claim 3, characterized in that, The ratio of polyvinylidene fluoride to N,N-dimethylacetamide is 1g:(8-12)mL.

8. A negative electrode, characterized in that, It includes the negative electrode current collector as described in any one of claims 1-2, and the negative electrode active material coated on the surface of the negative electrode current collector.

9. A lithium battery, characterized in that, Includes the negative electrode as described in claim 8.

10. An electrical device, characterized in that, Including the lithium battery as described in claim 9.

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