Preparation method of high-load NCM positive electrode based on SWCNT coated LLZO core-shell fiber non-woven fabric

Abstract

The invention discloses a preparation method of a high-load NCM positive electrode based on an SWCNT coated LLZO core-shell fiber non-woven fabric, and belongs to the technical field of lithium ion batteries. According to the invention, a single-walled carbon nanotube (SWCNT) fiber is used as a core, and a high-speed electron conduction path and mechanical support are provided; cubic-phase lithium lanthanum zirconium oxide (LLZO) is used as a'shell ', a high-speed ion conduction channel is provided, and physical isolation and chemical protection are carried out on an internal electronic path; preparing the core-shell fibers into a three-dimensional porous non-woven fabric skeleton through an electrostatic spinning or air laying technology; and finally, filling and fixing the high-nickel NCM ternary positive electrode active material in pores of the framework in a highly dense manner by means of solution permeation and in-situ thermal sintering to form the final composite positive electrode. Not only is the energy density of the battery improved, but also extremely high surface capacity and excellent rate capability and surface capacity can be realized.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method for preparing a high-load NCM cathode based on SWCNT@LLZO core-shell fiber nonwoven fabric. Background Technology

[0002] High-nickel layered oxides (such as LiNi) x Co y Mn z O2 (NCM, x+y+z=1) has become a key cathode material for achieving high energy density lithium-ion batteries due to its high specific capacity and relatively low cost. However, with the increasing market demand for long-lasting and lightweight batteries, there is an urgent need to develop materials with higher areal capacity (>4 mAh cm⁻¹). -2 The electrodes are typically produced by increasing the electrode compaction density or increasing the electrode thickness (i.e., high loading).

[0003] Currently, the traditional high-loading electrode preparation mainly involves mixing active materials, conductive agents (such as Super P and CNTs), and binders (such as PVDF) to form a slurry, which is then coated onto an aluminum foil current collector. This technical route has some inherent bottlenecks. As the electrode thickness increases, the electron transport path from the current collector to the surface of the active particles becomes longer, resulting in a significant increase in impedance. This leads to intensified electrode polarization, making it difficult to fully utilize the battery's designed capacity, and gradually reducing rate performance. Simultaneously, the solid-phase diffusion path of lithium ions in the electrolyte becomes tortuous and lengthy in thick electrodes, especially at high rates, where ion transport rate becomes a key factor limiting battery performance. Furthermore, during cycling, the large volume change of the active material in high-loading thick electrodes easily leads to cracking and peeling from the current collector, resulting in rapid capacity decay and shortened cycle life. Additionally, the intense side reactions between the high-nickel cathode and the electrolyte, and the difficulty in forming a uniform protective layer with binders and conductive agents in traditional slurry processes, also lead to interface instability, potentially consuming large amounts of lithium ions and causing rapid performance degradation.

[0004] To address these challenges, existing technologies have proposed several improvements, such as constructing three-dimensional current collectors: using porous materials like carbon nanotube sponges and graphene foams to replace traditional metal current collectors to shorten electron transport paths. However, these materials typically lack sufficient mechanical strength and cannot improve ion transport. Introducing solid-state electrolytes: using fast ion conductors like LLZO as coating layers or binder phases to improve interfacial ionic conductivity and suppress side reactions. However, traditional methods (such as ball milling) struggle to form continuous, uniform coating layers on the surface of active particles and do not contribute to electron conduction. Designing fiber electrodes: fabricating fiber membrane electrodes containing active materials using techniques such as electrospinning. However, such methods often struggle to simultaneously achieve a balance between high electronic conductivity, high ionic conductivity, and high active material loading. Therefore, there is an urgent need in this field for an innovative electrode structure design that can simultaneously solve the three core challenges of efficient electron and ion transport, mechanical stability, and interfacial stability under high loading. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-load NCM cathode based on SWCNT@LLZO core-shell fiber nonwoven fabric and its preparation method. This cathode constructs a unique three-dimensional interpenetrating network structure of "core-shell fiber skeleton + infiltration filling," aiming to simultaneously achieve ultra-high-speed, low-impedance dual continuous transport of electrons and ions; extremely high active material loading and areal capacity; excellent mechanical flexibility and structural integrity; and a stable and protected electrode-electrolyte interface. Its core lies in synthesizing a multi-layered, multifunctional composite structure: using single-walled carbon nanotube (SWCNT) fibers as the "core," providing a high-speed electron conduction pathway and mechanical support; using cubic lithium lanthanum zirconium oxide (LLZO) as the "shell," providing a high-speed ion conduction channel and physically isolating and chemically protecting the internal electron pathways; using electrospinning or airflow web forming technology to fabricate the core-shell fibers into a three-dimensional porous nonwoven fabric skeleton; finally, high-nickel NCM ternary cathode active material is highly densely filled and fixed in the pores of this skeleton through solution infiltration and in-situ thermal sintering, forming the final composite cathode.

[0006] This invention provides a method for preparing a high-load NCM cathode based on SWCNT@LLZO core-shell fiber nonwoven fabric, comprising the following steps: (1) Preparation of core-shell fiber precursor: Single-walled carbon nanotubes (SWCNTs) were dispersed in an organic solvent containing a surfactant to form a core-shell dispersion; cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12Targeting LLZO, lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in an ethanol / water mixture, and polyvinylpyrrolidone was added as a spinning aid. The mixture was stirred until a uniform and clear shell precursor solution was formed. Using coaxial electrospinning technology, the core dispersion and the shell precursor solution were injected into the inner and outer needles respectively for spinning to obtain SWCNT@LLZO precursor nonwoven film. (2) The SWCNT@LLZO precursor nonwoven film from step (1) is calcined in air to remove organic matter, and then calcined in an inert atmosphere to form a well-crystallized SWCNT@LLZO core-shell fiber skeleton. (3) Filling and fixing of NCM active material: The high-nickel NCM active material is mixed with the binder to form a slurry, which is then filled into the pores of the core-shell fiber skeleton by vacuum filtration. After the composite membrane is dried, it is heat-treated in an oxygen atmosphere to achieve firm fixation of NCM particles and interface stability.

[0007] In one embodiment of the present invention, in step (1), the surfactant is one of sodium dodecylbenzenesulfonate (SDBS), sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), and polyvinylpyrrolidone (PVP).

[0008] In one embodiment of the present invention, in step (1), the concentration of single-walled carbon nanotubes in the core layer dispersion is 0.3~1 mg / mL.

[0009] In one embodiment of the present invention, in step (1), the process parameters for electrospinning are: core flow rate 0.5~1.0 mL / h, shell flow rate 1~2 mL / h, voltage 15~30 kV, and receiving distance 10~20 cm.

[0010] In one embodiment of the present invention, in step (2), the organic matter is removed by calcination at 200-400 °C in an air atmosphere, and then by calcination at 700-900 °C in an inert atmosphere.

[0011] In one embodiment of the present invention, in step (3), the adhesive is one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and sodium alginate (SA).

[0012] In one embodiment of the present invention, in step (3), the high-nickel NCM active material and the binder are mixed at a mass ratio of (97~99):(3~1).

[0013] In one embodiment of the present invention, in step (3), the filtration conditions are -0.03 to -0.12 MPa.

[0014] In one embodiment of the present invention, in step (3), the conditions for heat treatment in an oxygen atmosphere are: heating to 400-600°C at a rate of 2-5 °C / min and holding for 2-4 h.

[0015] The present invention provides a high-load NCM cathode based on SWCNT@LLZO core-shell fiber nonwoven fabric prepared by the method described above.

[0016] The beneficial effects of this invention are: Compared with existing technologies, the high-load NCM cathode based on SWCNT@LLZO core-shell fiber nonwoven fabric provided by this invention can achieve an active material mass ratio of up to 98 wt%, far exceeding the 90-95 wt% of traditional slurry electrodes, due to the need for or minimal need for additional conductive agents and binders (<2 wt%), thereby directly improving the energy density of the battery. Simultaneously, through its unique dual-continuous three-dimensional conductive network structure, it can achieve extremely high areal capacity and excellent rate performance and areal capacity, exceeding 70 mg cm⁻¹. -2 With a high surface loading of active materials, the electrode's areal capacity can stably reach 9 mAh cm⁻¹. -2 Far exceeding the typical 4~6 mAh cm⁻¹ of commercially available thick electrodes. -2 The level of performance is achieved. Thanks to the excellent mechanical buffering capacity of the SWCNT@LLZO core-shell fiber framework structure, electrode structure pulverization and exfoliation are effectively suppressed, achieving high performance at 0.5C charge / discharge and greater than 10 mAh cm⁻¹. -2 Under the given areal capacity conditions, the capacity retention rate remains above 78% after 200 cycles. After 100 cycles, the high-frequency interfacial impedance (Rct) of the electrode of this invention increases by less than 60%, while the interfacial impedance of conventional electrodes typically increases by more than 100%. This quantifies the superior effect of the LLZO shell in stabilizing the electrode / electrolyte interface. Detailed Implementation

[0017] Method for assembling button cells: This patent uses a CR2032 coin cell for electrochemical performance testing. The specific assembly process is as follows: In a glove box filled with argon gas and containing less than 0.1 ppm of water and oxygen, the positive electrode shell and the working electrode (with an areal loading of 75~172 mg cm⁻¹) made by directly stamping the composite positive electrode material prepared according to the embodiments of this invention are assembled sequentially. -2The electrolyte (1 M LiPF6 dissolved in EC / DEC / EMC=1:1:1 system), Celgard 2400 polypropylene separator, metal Li sheet (which also serves as counter electrode and reference electrode), gasket and spring sheet are stacked in the negative electrode shell, and finally sealed by a sealing machine to complete the battery assembly.

[0018] Test methods and conditions for electrochemical performance: In this invention, after the assembled coin cells were left to stand and soak in the electrolyte for 12 hours, the following electrochemical tests were performed sequentially: using a testing system such as Xinwei, at 2.8-4.3 V (vs. Li) + Charge-discharge tests were conducted within the LLZO voltage range. First, the initial activation was performed with a current of 0.1C to obtain the initial coulombic efficiency and the initial areal capacity. Then, 200 cycles were performed at 0.5C to evaluate the capacity retention. Simultaneously, electrochemical impedance spectroscopy analysis was performed in an open-circuit state using the Chenhua electrochemical workstation. A frequency scan of 100 kHz to 10 mHz with an amplitude of 10 mV was applied. The interfacial impedance (Rct) was obtained by fitting the equivalent circuit. The increase in Rct after 100 cycles was examined to quantify the effect of the LLZO shell on improving interfacial stability.

[0019] Example 1 (1) Preparation of spinning solution: 10 mg SWCNT was dispersed in 20 mL of 1 wt% SDBS in DMF solution, sonicated for 6 h, and the supernatant was collected by centrifugation. This was used to synthesize 1 mmol of cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12 To target (LLZO), lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in 10 mL of ethanol / water (4:1) mixture, and 1 g of polyvinylpyrrolidone (PVP, M) was added. w ≈1300000) was used as a spinning aid, and the mixture was magnetically stirred at room temperature for 12 hours until a uniform and clear shell precursor solution was formed. The core layer (SWCNT dispersion) and the shell layer (LLZO precursor solution) were injected into the inner and outer needles of a coaxial electrospinning apparatus, respectively. The process parameters were set as follows: core layer flow rate of 0.8 mL / h, shell layer flow rate of 1.5 mL / h, applied voltage of 20 kV, and distance from the needle to the roller receiver of 15 cm. Spinning was carried out under these conditions to obtain an SWCNT@LLZO precursor nonwoven membrane.

[0020] (2) Heat treatment: The SWCNT@LLZO precursor membrane from step (1) was calcined at 300°C for 3 hours in air to completely remove PVP and organic solvents. Subsequently, the precursor nonwoven membrane was calcined at 850°C for 5 hours in Ar atmosphere to obtain a well-crystallized SWCNT@LLZO core-shell fiber skeleton.

[0021] (3) NCM filling: Commercial high-nickel NCM secondary spherical particles (LiNi) are filled. 0.8 Co 0.1 Mn 0.1 O2, NCM811 (purchased from Shenzhen Kejing), and polyvinylidene fluoride (PVDF) adhesive were mixed at a mass ratio of 98:2. First, PVDF powder was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) solvent to prepare a clear slurry with a concentration of 5 wt%. Then, NCM811 powder was gradually added to the PVDF slurry, controlling the total solid content of the slurry to 70 wt%. A SWCNT@LLZO core-shell fiber nonwoven fabric skeleton (approximately 5 cm × 5 cm) was cut, fixed in a Buchner funnel, and connected to a vacuum filtration device, maintaining the system pressure at -0.05 MPa. The prepared NCM 811 slurry was slowly and evenly dripped onto the entire surface of the nonwoven fabric skeleton using a dropper. Under negative pressure, the slurry was rapidly and thoroughly drawn into and filled into the pores of the three-dimensional porous network of the skeleton. This process was repeated three times until the skeleton pores were completely filled and no obvious slurry residue remained on the surface. The impregnated composite membrane was vacuum dried at 80°C for 12 h to remove NMP solvent. Then, under an O2 atmosphere, the temperature was increased to 500°C at 2 °C / min and held for 3 h, followed by cooling to room temperature.

[0022] Example 2 (1) Preparation of spinning solution: 10 mg SWCNT was dispersed in 20 mL of 1 wt% SDBS in DMF solution, sonicated for 6 h, and the supernatant was collected by centrifugation. This was used to synthesize 1 mmol of cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12 To target (LLZO), lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in 10 mL of ethanol / water (4:1) mixture, and 1 g of polyvinylpyrrolidone (PVP, M) was added. w≈1300000) was used as a spinning aid, and the mixture was magnetically stirred at room temperature for 12 hours until a uniform and clear shell precursor solution was formed. The core layer (SWCNT dispersion) and the shell layer (LLZO precursor solution) were injected into the inner and outer needles of a coaxial electrospinning apparatus, respectively. The process parameters were set as follows: core layer flow rate of 0.8 mL / h, shell layer flow rate of 1.5 mL / h, applied voltage of 20 kV, and distance from the needle to the roller receiver of 15 cm. Spinning was carried out under these conditions to obtain an SWCNT@LLZO precursor nonwoven membrane.

[0023] (2) Heat treatment: The SWCNT@LLZO precursor membrane from step (1) was calcined at 300°C for 3 hours in air to completely remove PVP and organic solvents. Subsequently, the precursor nonwoven membrane was calcined at 850°C for 5 hours in Ar atmosphere to obtain a well-crystallized SWCNT@LLZO core-shell fiber skeleton.

[0024] (3) NCM filling: Commercial high-nickel NCM secondary spherical particles (LiNi) are filled. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 98:2. First, PVDF powder was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) solvent to prepare a clear slurry with a concentration of 5 wt%. Then, NCM811 powder was gradually added to the PVDF slurry, controlling the total solid content of the slurry to 70 wt%. A SWCNT@LLZO core-shell fiber nonwoven fabric skeleton (approximately 5 cm × 5 cm) was cut, fixed in a Buchner funnel, and connected to a vacuum filtration device, maintaining the system pressure at -0.03 MPa. The prepared NCM 811 slurry was slowly and evenly dripped onto the entire surface of the nonwoven fabric skeleton using a dropper. Under negative pressure, the slurry was rapidly and thoroughly drawn into and filled into the pores of the three-dimensional porous network of the skeleton. This process was repeated three times until the pores of the skeleton were completely filled and no obvious slurry residue remained on the surface. The impregnated composite membrane was vacuum dried at 80°C for 12 h to remove NMP solvent. Then, under an O2 atmosphere, the temperature was increased to 500°C at 2 °C / min and held for 3 h, followed by cooling to room temperature.

[0025] Example 3 (1) Preparation of spinning solution: 10 mg SWCNT was dispersed in 20 mL of 1 wt% SDBS in DMF solution, sonicated for 6 h, and the supernatant was collected by centrifugation. This was used to synthesize 1 mmol of cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12To target (LLZO), lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in 10 mL of ethanol / water (4:1) mixture, and 1 g of polyvinylpyrrolidone (PVP, M) was added. w ≈1300000) was used as a spinning aid, and the mixture was magnetically stirred at room temperature for 12 hours until a uniform and clear shell precursor solution was formed. The core layer (SWCNT dispersion) and the shell layer (LLZO precursor solution) were injected into the inner and outer needles of a coaxial electrospinning apparatus, respectively. The process parameters were set as follows: core layer flow rate of 0.8 mL / h, shell layer flow rate of 1.5 mL / h, applied voltage of 20 kV, and distance from the needle to the roller receiver of 15 cm. Spinning was carried out under these conditions to obtain an SWCNT@LLZO precursor nonwoven membrane.

[0026] (2) Heat treatment: The SWCNT@LLZO precursor membrane from step (1) was calcined at 300°C for 3 hours in air to completely remove PVP and organic solvents. Subsequently, the precursor nonwoven membrane was calcined at 850°C for 5 hours in Ar atmosphere to obtain a well-crystallized SWCNT@LLZO core-shell fiber skeleton.

[0027] (3) NCM filling: Commercial high-nickel NCM secondary spherical particles (LiNi) are filled. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 98:2. First, PVDF powder was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) solvent to prepare a clear slurry with a concentration of 5 wt%. Then, NCM811 powder was gradually added to the PVDF slurry, controlling the total solid content of the slurry to 70 wt%. A SWCNT@LLZO core-shell fiber nonwoven fabric skeleton (approximately 5 cm × 5 cm) was cut, fixed in a Buchner funnel, and connected to a vacuum filtration device, maintaining the system pressure at -0.08 MPa. The prepared NCM 811 slurry was slowly and evenly dripped onto the entire surface of the nonwoven fabric skeleton using a dropper. Under negative pressure, the slurry was rapidly and thoroughly drawn into and filled into the pores of the three-dimensional porous network of the skeleton. This process was repeated three times until the skeleton pores were completely filled and no obvious slurry residue remained on the surface. The impregnated composite membrane was vacuum dried at 80°C for 12 h to remove NMP solvent. Then, under an O2 atmosphere, the temperature was increased to 500°C at 2 °C / min and held for 3 h, followed by cooling to room temperature.

[0028] Example 4 (1) Preparation of spinning solution: 10 mg SWCNT was dispersed in 20 mL of 1 wt% SDBS in DMF solution, sonicated for 6 h, and the supernatant was collected by centrifugation. This was used to synthesize 1 mmol of cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12 To target (LLZO), lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in 10 mL of ethanol / water (4:1) mixture, and 1 g of polyvinylpyrrolidone (PVP, M) was added. w ≈1300000) was used as a spinning aid, and the mixture was magnetically stirred at room temperature for 12 hours until a uniform and clear shell precursor solution was formed. The core layer (SWCNT dispersion) and the shell layer (LLZO precursor solution) were injected into the inner and outer needles of a coaxial electrospinning apparatus, respectively. The process parameters were set as follows: core layer flow rate of 0.8 mL / h, shell layer flow rate of 1.5 mL / h, applied voltage of 20 kV, and distance from the needle to the roller receiver of 15 cm. Spinning was carried out under these conditions to obtain an SWCNT@LLZO precursor nonwoven membrane.

[0029] (2) Heat treatment: The SWCNT@LLZO precursor membrane from step (1) was calcined at 300°C for 3 hours in air to completely remove PVP and organic solvents. Subsequently, the precursor nonwoven membrane was calcined at 850°C for 5 hours in Ar atmosphere to obtain a well-crystallized SWCNT@LLZO core-shell fiber skeleton.

[0030] (3) NCM filling: Commercial high-nickel NCM secondary spherical particles (LiNi) are filled. 0.8 Co 0.1 Mn 0.1O2 (NCM811) and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 98:2. First, PVDF powder was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) solvent to prepare a clear slurry with a concentration of 5 wt%. Then, NCM811 powder was gradually added to the PVDF slurry, controlling the total solid content of the slurry to 70 wt%. A SWCNT@LLZO core-shell fiber nonwoven fabric skeleton (approximately 5 cm × 5 cm) was cut, fixed in a Buchner funnel, and connected to a vacuum filtration device, maintaining the system pressure at -0.12 MPa. The prepared NCM 811 slurry was slowly and evenly dripped onto the entire surface of the nonwoven fabric skeleton using a dropper. Under negative pressure, the slurry was rapidly and thoroughly drawn into and filled into the pores of the three-dimensional porous network of the skeleton. This process was repeated three times until the skeleton pores were completely filled and no obvious slurry residue remained on the surface. The impregnated composite membrane was vacuum dried at 80°C for 12 h to remove NMP solvent. Then, under an O2 atmosphere, the temperature was increased to 500°C at 2 °C / min and held for 3 h, followed by cooling to room temperature.

[0031] Example 5 (1) Preparation of spinning solution: 10 mg SWCNT was dispersed in 20 mL of 1 wt% SDBS in DMF solution, sonicated for 6 h, and the supernatant was collected by centrifugation. This was used to synthesize 1 mmol of cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12 To target (LLZO), lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in 10 mL of ethanol / water (4:1) mixture, and 1 g of polyvinylpyrrolidone (PVP, M) was added. w ≈1300000) was used as a spinning aid, and the mixture was magnetically stirred at room temperature for 12 hours until a uniform and clear shell precursor solution was formed. The core layer (SWCNT dispersion) and the shell layer (LLZO precursor solution) were injected into the inner and outer needles of a coaxial electrospinning apparatus, respectively. The process parameters were set as follows: core layer flow rate of 0.8 mL / h, shell layer flow rate of 1.5 mL / h, applied voltage of 20 kV, and distance from the needle to the roller receiver of 15 cm. Spinning was carried out under these conditions to obtain an SWCNT@LLZO precursor nonwoven membrane.

[0032] (2) Heat treatment: The SWCNT@LLZO precursor membrane from step (1) was calcined at 300°C for 3 hours in air to completely remove PVP and organic solvents. Subsequently, the precursor nonwoven membrane was calcined at 850°C for 5 hours in Ar atmosphere to obtain a well-crystallized SWCNT@LLZO core-shell fiber skeleton.

[0033] (3) NCM filling: Commercial high-nickel NCM secondary spherical particles (LiNi) are filled. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 98:2. First, PVDF powder was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) solvent to prepare a clear slurry with a concentration of 5 wt%. Then, NCM811 powder was gradually added to the PVDF slurry, controlling the total solid content of the slurry to be 70 wt%. A SWCNT@LLZO core-shell fiber nonwoven fabric skeleton (approximately 5 cm × 5 cm) was cut, fixed in a Buchner funnel, and connected to a vacuum filtration device, maintaining the system pressure at -0.05 MPa. The prepared NCM 811 slurry was slowly and evenly dripped onto the entire surface of the nonwoven fabric skeleton using a dropper. Under negative pressure, the slurry was rapidly and thoroughly drawn into and filled into the pores of the three-dimensional porous network of the skeleton. This process was repeated three times until the pores of the skeleton were completely filled and no obvious slurry residue remained on the surface. The impregnated composite membrane was vacuum dried at 80°C for 12 h to remove NMP solvent. Then, under an O2 atmosphere, the temperature was increased to 500°C at 5 °C / min and held for 3 h, followed by cooling to room temperature.

[0034] Example 6 (1) Preparation of spinning solution: 10 mg SWCNT was dispersed in 20 mL of 1 wt% SDBS in DMF solution, sonicated for 6 h, and the supernatant was collected by centrifugation. This was used to synthesize 1 mmol of cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12 To target (LLZO), lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in 10 mL of ethanol / water (4:1) mixture, and 1 g of polyvinylpyrrolidone (PVP, M) was added. w≈1300000) was used as a spinning aid, and the mixture was magnetically stirred at room temperature for 12 hours until a uniform and clear shell precursor solution was formed. The core layer (SWCNT dispersion) and the shell layer (LLZO precursor solution) were injected into the inner and outer needles of a coaxial electrospinning apparatus, respectively. The process parameters were set as follows: core layer flow rate of 0.8 mL / h, shell layer flow rate of 1.5 mL / h, applied voltage of 20 kV, and distance from the needle to the roller receiver of 15 cm. Spinning was carried out under these conditions to obtain an SWCNT@LLZO precursor nonwoven membrane.

[0035] (2) Heat treatment: The SWCNT@LLZO precursor membrane from step (1) was calcined at 300°C for 3 hours in air to completely remove PVP and organic solvents. Subsequently, the precursor nonwoven membrane was calcined at 850°C for 5 hours in Ar atmosphere to obtain a well-crystallized SWCNT@LLZO core-shell fiber skeleton.

[0036] (3) NCM filling: Commercial high-nickel NCM secondary spherical particles (LiNi) are filled. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 98:2. First, PVDF powder was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) solvent to prepare a clear slurry with a concentration of 5 wt%. Then, NCM811 powder was gradually added to the PVDF slurry, controlling the total solid content of the slurry to be 70 wt%. A SWCNT@LLZO core-shell fiber nonwoven fabric skeleton (approximately 5 cm × 5 cm) was cut, fixed in a Buchner funnel, and connected to a vacuum filtration device, maintaining the system pressure at -0.05 MPa. The prepared NCM 811 slurry was slowly and evenly dripped onto the entire surface of the nonwoven fabric skeleton using a dropper. Under negative pressure, the slurry was rapidly and thoroughly drawn into and filled into the pores of the three-dimensional porous network of the skeleton. This process was repeated three times until the pores of the skeleton were completely filled and no obvious slurry residue remained on the surface. The impregnated composite membrane was vacuum dried at 80°C for 12 h to remove NMP solvent. Then, under an O2 atmosphere, the temperature was increased to 400°C at 2 °C / min and held for 3 h, followed by cooling to room temperature.

[0037] Example 7 (1) Preparation of spinning solution: 10 mg SWCNT was dispersed in 20 mL of 1 wt% SDBS in DMF solution, sonicated for 6 h, and the supernatant was collected by centrifugation. This was used to synthesize 1 mmol of cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12To target (LLZO), lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in 10 mL of ethanol / water (4:1) mixture, and 1 g of polyvinylpyrrolidone (PVP, M) was added. w ≈1300000) was used as a spinning aid, and the mixture was magnetically stirred at room temperature for 12 hours until a uniform and clear shell precursor solution was formed. The core layer (SWCNT dispersion) and the shell layer (LLZO precursor solution) were injected into the inner and outer needles of a coaxial electrospinning apparatus, respectively. The process parameters were set as follows: core layer flow rate of 0.8 mL / h, shell layer flow rate of 1.5 mL / h, applied voltage of 20 kV, and distance from the needle to the roller receiver of 15 cm. Spinning was carried out under these conditions to obtain an SWCNT@LLZO precursor nonwoven membrane.

[0038] (2) Heat treatment: The SWCNT@LLZO precursor membrane from step (1) was calcined at 300°C for 3 hours in air to completely remove PVP and organic solvents. Subsequently, the precursor nonwoven membrane was calcined at 850°C for 5 hours in Ar atmosphere to obtain a well-crystallized SWCNT@LLZO core-shell fiber skeleton.

[0039] (3) NCM filling: Commercial high-nickel NCM secondary spherical particles (LiNi) are filled. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 98:2. First, PVDF powder was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) solvent to prepare a clear slurry with a concentration of 5 wt%. Then, NCM811 powder was gradually added to the PVDF slurry, controlling the total solid content of the slurry to 70 wt%. A SWCNT@LLZO core-shell fiber nonwoven fabric skeleton (approximately 5 cm × 5 cm) was cut, fixed in a Buchner funnel, and connected to a vacuum filtration device, maintaining the system pressure at -0.10 MPa. The prepared NCM 811 slurry was slowly and evenly dripped onto the entire surface of the nonwoven fabric skeleton using a dropper. Under negative pressure, the slurry was rapidly and thoroughly drawn into and filled into the pores of the three-dimensional porous network of the skeleton. This process was repeated three times until the pores of the skeleton were completely filled and no obvious slurry residue remained on the surface. The impregnated composite membrane was vacuum dried at 80°C for 12 h to remove NMP solvent. Then, under an O2 atmosphere, the temperature was increased to 600°C at 2 °C / min and held for 3 h, followed by cooling to room temperature.

[0040] Example 8 (1) Preparation of spinning solution: 10 mg SWCNT was dispersed in 20 mL of 1 wt% SDBS in DMF solution, sonicated for 6 h, and the supernatant was collected by centrifugation. This was used to synthesize 1 mmol of cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12 To target (LLZO), lithium nitrate (LiNO3), lanthanum nitrate hexahydrate (La(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), and tantalum ethoxide (Ta(OC2H5)5) were weighed according to the stoichiometric ratio, dissolved in 10 mL of ethanol / water (4:1) mixture, and 1 g of polyvinylpyrrolidone (PVP, M) was added. w ≈1300000) was used as a spinning aid, and the mixture was magnetically stirred at room temperature for 12 hours until a uniform and clear shell precursor solution was formed. The core layer (SWCNT dispersion) and the shell layer (LLZO precursor solution) were injected into the inner and outer needles of a coaxial electrospinning apparatus, respectively. The process parameters were set as follows: core layer flow rate of 0.8 mL / h, shell layer flow rate of 1.5 mL / h, applied voltage of 20 kV, and distance from the needle to the roller receiver of 15 cm. Spinning was carried out under these conditions to obtain an SWCNT@LLZO precursor nonwoven membrane.

[0041] (2) Heat treatment: The SWCNT@LLZO precursor membrane from step (1) was calcined at 300°C for 3 hours in air to completely remove PVP and organic solvents. Subsequently, the precursor nonwoven membrane was calcined at 850°C for 5 hours in Ar atmosphere to obtain a well-crystallized SWCNT@LLZO core-shell fiber skeleton.

[0042] (3) NCM filling: Commercial high-nickel NCM secondary spherical particles (LiNi) are filled. 0.8 Co 0.1 Mn 0.1O2 (NCM811) and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 98:2. First, PVDF powder was dissolved in an appropriate amount of N-methylpyrrolidone (NMP) solvent to prepare a clear slurry with a concentration of 5 wt%. Then, NCM811 powder was gradually added to the PVDF slurry, controlling the total solid content of the slurry to 70 wt%. A SWCNT@LLZO core-shell fiber nonwoven fabric skeleton (approximately 5 cm × 5 cm) was cut, fixed in a Buchner funnel, and connected to a vacuum filtration device, maintaining the system pressure at -0.08 MPa. The prepared NCM 811 slurry was slowly and evenly dripped onto the entire surface of the nonwoven fabric skeleton using a dropper. Under negative pressure, the slurry was rapidly and thoroughly drawn into and filled into the pores of the three-dimensional porous network of the skeleton. This process could be repeated 3 times until the skeleton pores were completely filled and no obvious slurry residue remained on the surface. The impregnated composite membrane was vacuum dried at 80°C for 12 h to remove NMP solvent. Then, under an O2 atmosphere, the temperature was increased to 600°C at 5 °C / min and held for 3 h, followed by cooling to room temperature.

[0043] Table 1 systematically lists the key process parameters used in each embodiment of the present invention and their corresponding positive electrode active material surface loading. The data shows that by adjusting the vacuum filtration pressure, the positive electrode surface loading can be effectively maintained between 82 and 115 mg / cm³. - The pressure can be precisely adjusted within a wide range. Specifically, the filtration pressure shows a positive correlation with the loading (Examples 1, 2, and 3), demonstrating the effectiveness and controllability of this preparation method in achieving high loading. Meanwhile, different heat treatment temperatures and times (Examples 5-8) have relatively little impact on the final loading, indicating that the skeleton structure maintains a stable loading capacity under different post-treatment conditions.

[0044] Table 2 shows the electrochemical performance of coin cells assembled using the cathodes from the above embodiments. These data are highly correlated with the process parameters and loading in Table 1, and all embodiments exhibit high areal capacities (8.8-13.2 mAh cm⁻¹). -2 Furthermore, this value is directly related to the load in Table 1. Even under these extremely high loads, the capacity retention rate remains at a high level, which strongly confirms the key role of the SWCNT@LLZO three-dimensional dual-continuous conduction network in alleviating transmission bottlenecks and ensuring structural stability.

[0045] Table 1 shows the NCM load in the examples.

[0046] Table 2 shows the performance comparison of the embodiments of the present invention after assembling a coin cell with metallic Li as the counter electrode.

[0047]

[0048] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a high-loading NCM cathode based on SWCNT@LLZO core-shell fiber nonwoven fabric, characterized in that, Includes the following steps: (1) Preparation of core-shell fiber precursor: Single-walled carbon nanotubes were dispersed in an organic solvent containing a surfactant to form a core-shell dispersion; cubic Li 6.4 La3Zr 1.4 Ta 0.6 O 12 To achieve the desired result, lithium nitrate, lanthanum nitrate hexahydrate, zirconium oxychloride octahydrate, and tantalum ethoxide were weighed according to the specified ratio, dissolved in an ethanol / water mixture, and polyvinylpyrrolidone was added as a spinning aid. The mixture was stirred until a uniform and clear shell precursor solution was formed. Using coaxial electrospinning technology, the core dispersion and the shell precursor solution were injected into the inner and outer needles respectively for spinning to obtain the SWCNT@LLZO precursor nonwoven membrane. (2) The SWCNT@LLZO precursor nonwoven membrane from step (1) is calcined in air to remove organic matter, and then calcined in an inert atmosphere to form a SWCNT@LLZO core-shell fiber skeleton. (3) Filling and fixing of NCM active material: The high-nickel NCM active material is mixed with the binder to form a slurry, which is then filled into the pores of the core-shell fiber skeleton by vacuum filtration. After the composite membrane is dried, it is heat-treated in an oxygen atmosphere to achieve firm fixation of NCM particles and interface stability.

2. The method according to claim 1, characterized in that, In step (1), the surfactant is one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and polyvinylpyrrolidone.

3. The method according to claim 1, characterized in that, In step (1), the concentration of single-walled carbon nanotubes in the core layer dispersion is 0.3~1 mg / mL.

4. The method according to claim 1, characterized in that, In step (1), the electrospinning process parameters are: core flow rate 0.5~1.0 mL / h, shell flow rate 1~2 mL / h, voltage 15~30 kV, and receiving distance 10~20 cm.

5. The method according to claim 1, characterized in that, In step (2), the organic matter is removed by calcination at 200-400°C in an air atmosphere, and then by calcination at 700-900°C in an inert atmosphere.

6. The method according to claim 1, characterized in that, In step (3), the adhesive is one of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, and sodium alginate.

7. The method according to claim 1, characterized in that, In step (3), the high-nickel NCM active material and the binder are mixed at a mass ratio of 97~99:3~1.

8. The method according to claim 1, characterized in that, In step (3), the filtration conditions are -0.12 to -0.03 MPa.

9. The method according to claim 1, characterized in that, In step (3), the conditions for heat treatment in an oxygen atmosphere are: heating to 400-600°C at a rate of 2-5 °C / min and holding for 2-4 h.

10. The high-load NCM cathode based on SWCNT@LLZO core-shell fiber nonwoven fabric prepared by the method of any one of claims 1 to 9.

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